Method for inter prediction and device therefor, and method for motion compensation and device therefor

ABSTRACT

Provided are an inter prediction method and a motion compensation method. The inter prediction method includes: performing inter prediction on a current image by using a long-term reference image stored in a decoded picture buffer; determining residual data and a motion vector of the current image generated via the inter prediction; and determining least significant bit (LSB) information as a long-term reference index indicating the long-term reference image by dividing picture order count (POC) information of the long-term reference image into most significant bit (MSB) information and the LSB information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/354,721 filed Apr. 28, 2014, which is U.S. National Stage ofInternational Application No. PCT/KR2012/008946 having an InternationalFiling Date of Oct. 29, 2012, which claims the benefit of U.S.Provisional Application No. 61/552,698 filed Oct. 28, 2011. The entiredisclosures of the prior applications are considered part of thedisclosure of the accompanying continuation, and are hereby incorporatedby reference.

TECHNICAL FIELD

The present invention relates to an inter prediction method and a motioncompensation method.

BACKGROUND ART

As hardware for reproducing and storing high resolution or high qualityvideo content is being developed and supplied, a need for a video codecfor effectively encoding or decoding the high resolution or high qualityvideo content is increasing. According to a conventional video codec, avideo is encoded according to a limited encoding method based on amacroblock having a predetermined size.

Image data of a spatial region is transformed into coefficients of afrequency region via frequency transformation. According to a videocodec, an image is split into blocks having a predetermined size,discrete cosine transformation (DCT) is performed on each block, andfrequency coefficients are encoded in block units, for rapid calculationof frequency transformation. Compared with image data of a spatialregion, coefficients of a frequency region are easily compressed. Inparticular, since an image pixel value of a spatial region is expressedaccording to a prediction error via inter prediction or intra predictionof a video codec, when frequency transformation is performed on theprediction error, a large amount of data may be transformed to 0.According to a video codec, an amount of data may be reduced byreplacing data that is consecutively and repeatedly generated withsmall-sized data.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present invention provides an inter prediction method and an interprediction apparatus, which use a long-term reference image, and amotion compensation method and a motion compensation apparatus, whichuse a long-term reference image. The present invention also provides avideo encoding method and a video encoding apparatus, which involveinter prediction and motion compensation using a long-term referenceimage, and a video decoding method and a video decoding apparatus, whichinvolve motion compensation using a long-term reference image.

Technical Solution

According to an aspect of the present invention, there is provided aninter prediction method including: performing inter prediction on acurrent image by using a long-term reference image stored in a decodedpicture buffer; determining residual data and a motion vector of thecurrent image generated via the inter prediction; and determining leastsignificant bit (LSB) information as a long-term reference indexindicating the long-term reference image by dividing picture order count(POC) information of the long-term reference image into most significantbit (MSB) information and the LSB information.

Advantageous Effects

According to a motion compensation method of the present invention,least significant bit (LSB) information of picture order count (POC)information of a long-term reference image may be used as a referenceindex indicating a long-term reference image among reference images usedfor inter prediction of an image. A long-term reference image may beindicated by using POC information of an image without having to useseparate image numbers for long-term reference images in order toidentify the long-term reference images. Accordingly, no storage spacefor storing the separate image numbers for the long-term referenceimages may be spared. Also, a range of indexes indicating the long-termreference images may be infinite.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of an inter prediction apparatus according toan embodiment of the present invention;

FIG. 1B is a flowchart illustrating an inter prediction method accordingto an embodiment of the present invention;

FIG. 2A is a block diagram of a motion compensation apparatus accordingto an embodiment of the present invention;

FIG. 2B is a flowchart illustrating a motion compensation methodaccording to an embodiment of the present invention;

FIG. 3 is a table showing least significant bit (LSB) information andmost significant bit (MSB) information of picture order count (POC)information of a long-term reference image, according to an embodimentof the present invention;

FIG. 4 is a block diagram of a video encoding apparatus that performsinter prediction, according to an embodiment of the present invention;

FIG. 5 is a block diagram of a video decoding apparatus that performsmotion compensation, according to an embodiment of the presentinvention;

FIG. 6 is a block diagram of a video encoding apparatus based on codingunits according to a tree structure, according to an embodiment of thepresent invention;

FIG. 7 is a block diagram of a video decoding apparatus based on codingunits according to a tree structure, according to an embodiment of thepresent invention;

FIG. 8 is a diagram for describing a concept of coding units accordingto an embodiment of the present invention;

FIG. 9 is a block diagram of an image encoder based on coding units,according to an embodiment of the present invention;

FIG. 10 is a block diagram of an image decoder based on coding units,according to an embodiment of the present invention;

FIG. 11 is a diagram illustrating deeper coding units according todepths, and partitions, according to an embodiment of the presentinvention;

FIG. 12 is a diagram for describing a relationship between a coding unitand transformation units, according to an embodiment of the presentinvention;

FIG. 13 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an embodiment of thepresent invention;

FIG. 14 is a diagram of deeper coding units according to depths,according to an embodiment of the present invention;

FIGS. 15 through 17 are diagrams for describing a relationship betweencoding units, prediction units, and transformation units, according toan embodiment of the present invention;

FIG. 18 is a diagram for describing a relationship between a codingunit, a prediction unit, and a transformation unit, according toencoding mode information of Table 1;

FIG. 19 is a diagram of a physical structure of a disc in which aprogram is stored, according to an embodiment of the present invention;

FIG. 20 is a diagram of a disc drive for recording and reading a programby using a disc;

FIG. 21 is a diagram of an overall structure of a content supply systemfor providing a content distribution service;

FIGS. 22 and 23 are diagrams respectively of an external structure andan internal structure of a mobile phone to which a video encoding methodand a video decoding method are applied, according to an embodiment ofthe present invention;

FIG. 24 is a diagram of a digital broadcast system to which acommunication system is applied, according to an embodiment of thepresent invention; and

FIG. 25 is a diagram illustrating a network structure of a cloudcomputing system using a video encoding apparatus and a video decodingapparatus, according to an embodiment of the present invention.

BEST MODE

According to an aspect according to the present invention, there isprovided an inter prediction method including: performing interprediction on a current image by using a long-term reference imagestored in a decoded picture buffer; determining residual data and amotion vector of the current image generated via the inter prediction;and determining least significant bit (LSB) information as a long-termreference index indicating the long-term reference image by dividingpicture order count (POC) information of the long-term reference imageinto most significant bit (MSB) information and the LSB information.

The determining of the LSB information may include inserting LSBinformation of POC information of a long-term reference image used forinter prediction of a current slice into a slice header, as thelong-term reference index.

The determining of the LSB information may include dividing differenceinformation between POC information of the current image and the POCinformation of the long-term reference image into MSB information andLSB information to determine the LSB information of the differenceinformation as the long-term reference index.

The inter prediction method may further include: performing interprediction on the current image by using a short-term reference imagestored in the decoded picture buffer; and determining LSB information ofPOC information of the short-term reference image as a short-termreference index indicating the short-term reference image.

The determining of the residual data and the motion vector may includedetermining the residual data and the motion vector according to blocksof the current image, based on results of inter prediction performedaccording to the blocks of the current image.

According to another aspect according to the present invention, there isprovided a motion compensation method including: receiving encoded imagedata, a motion vector, and a long-term reference index; restoringresidual data of a current image by decoding the encoded image data;determining picture order count (POC) information by using mostsignificant bit (MSB) information and least significant bit (LSB)information of a long-term reference image of the current image byreading the LSB information of the POC information of the long-termreference image from the long-term reference index; and restoring thecurrent image by performing motion compensation using the motion vectorand the residual data based on the long-term reference imagecorresponding to the determined POC information from among referenceimages stored in a decoded picture buffer.

The determining of the POC information may include: predicting MSBinformation of POC information of a second long-term reference imagefrom MSB information of POC information of a first long-term referenceimage, from among a plurality of long-term reference images for thecurrent image; and restoring the POC information of the second long-termreference image by composing LSB information of the POC information ofthe second long-term reference image read from the received long-termreference index, and the MSB information of the POC information of thesecond long-term reference image.

The determining of the POC information may include: restoring differenceinformation between POC information of the current image and the POCinformation of the long-term reference image by composing the MSBinformation and the LSB information of the POC information of thelong-term reference image; and determining a POC number of the long-termreference image by adding or subtracting the difference information toor from the POC information of the current image.

The receiving may include parsing the long-term reference indexindicating a long-term reference image for motion compensation of acurrent slice from a slice header.

The motion compensation method may further include: receiving ashort-term reference index for inter prediction of the current image;reading LSB information of POC information of a short-term referenceimage for inter prediction of the current image, from the short-termreference index; determining the POC information of the short-termreference image by using the read LSB information of the short-termreference image and MSB information of a previous short-term referenceimage; and performing motion compensation on the current image by usingthe short-term reference image corresponding to the determined POCinformation from among reference images stored in the decoded picturebuffer.

The receiving may include receiving the encoded image data according toblocks of the current image, the restoring of the residual data mayinclude restoring the residual data and the motion vector according tothe blocks, and the restoring of the current image may include restoringthe current image by performing motion compensation using the residualdata and the motion vector according to the blocks.

According to another aspect according to the present invention, there isprovided an inter prediction apparatus including: an inter predictionunit for performing inter prediction on a current image by using along-term reference image stored in a decoded picture buffer; an outputunit for outputting least significant bit (LSB) information as along-term reference index indicating the long-term reference image bydividing picture order count (POC) information of the long-termreference image into most significant bit (MSB) information and the LSBinformation, and outputting residual data and a motion vector of thecurrent image generated via the inter prediction.

According to another aspect according to the present invention, there isprovided a motion compensation apparatus including: a receiving unit forreceiving encoded image data, a motion vector, and a long-term referenceindex; and a motion compensation unit for restoring residual data of acurrent image by decoding the encoded image data, reading leastsignificant bit (LSB) information of picture order count (POC)information of a long-term reference image of the current image from thelong-term reference index, determining the POC information by using mostsignificant bit (MSB) information and the LSB information of thelong-term reference image, and restoring the current image by performingmotion compensation using the motion vector and the residual data basedon the long-term reference image corresponding to the determined POCinformation from among reference images stored in a decoded picturebuffer.

According to another aspect according to the present invention, there isprovided a computer-readable recording medium having recorded thereon aprogram for executing the inter prediction method.

According to another aspect according to the present invention, there isprovided a computer-readable recording medium having recorded thereon aprogram for executing the motion compensation method.

According to another aspect according to the present invention, there isprovided a video encoding apparatus including: a decoded picture bufferfor storing reference images for inter prediction of an image; an interprediction unit for generating residual data by performing interprediction on a current image by using a long-term reference imagestored in the decoded picture buffer; a transformation quantization unitfor generating a quantized transformation coefficient by performingtransformation and quantization on the residual data; and an entropyencoding unit for performing entropy encoding on least significant bit(LSB) information that is a long-term reference index indicating thelong-term reference image, and symbols including the quantizedtransformation coefficient and a motion vector by dividing picture ordercount (POC) information of the long-term reference image into mostsignificant bit (MSB) information and the LSB information.

According to another aspect according to the present invention, there isprovided a video decoding apparatus including: a receiving unit forreceiving a video stream and parsing encoded image data, a motionvector, and a long-term reference index by performing entropy decodingon the received video stream; an inverse quantization and inversetransformation unit for restoring residual data by performing inversequantization and inverse transformation on the encoded image data; adecoded picture buffer for storing reference images for motioncompensation; a motion compensation unit for restoring residual data ofa current image by decoding the encoded image data, reading leastsignificant bit (LSB) information of picture order count (POC)information of a long-term reference image of the current image from thelong-term reference index, determining the POC information by using mostsignificant bit (MSB) information and the LSB information of thelong-term reference image, and performing motion compensation using themotion vector and the residual data based on the long-term referenceimage corresponding to the determined POC information from amongreference images stored in the decoded picture buffer; and an in-loopfiltering unit for performing deblocking filtering on a restored imagegenerated via the motion compensation.

MODE OF THE INVENTION

Hereinafter, an inter prediction method and an inter predictionapparatus, and a motion compensation method and a motion compensationapparatus, which use a long-term reference image, according toembodiments of the present invention, will be described with referenceto FIGS. 1 through 3. Also, a video encoding apparatus that performsinter prediction and a video decoding apparatus that performs motioncompensation, according to embodiments of the present invention, will bedescribed with reference to FIGS. 4 and 5. Also, a video encodingtechnique and a video decoding technique involving inter predictionbased on coding units having a tree structure, according to embodimentsof the present invention, will be described with reference to FIGS. 6through 18. Hereinafter, an ‘image’ may denote a still image or a movingimage of a video, or a video itself.

First, an inter prediction method and an inter prediction apparatus,which use a long-term reference image, according to embodiments of thepresent invention, will be described with reference to FIGS. 1A through3. Then, a video encoding method and a video decoding method, whichinvolve inter prediction, according to embodiments of the presentinvention, will be described with reference to FIGS. 4 and 5.

FIG. 1A is a block diagram of an inter prediction apparatus 10 accordingto an embodiment of the present invention.

The inter prediction apparatus 10 includes an inter prediction unit 12and an output unit 14.

Inter prediction uses similarity between a current image and anotherimage. A reference region similar to a current region of the currentimage is detected from a reference image restored before the currentimage. A distance between the current region and the reference region oncoordinates is expressed in a motion vector, and a difference betweenpixel values of the current region and the reference region is expressedas residual data. Accordingly, instead of directly outputting imageinformation of the current region, an index indicating the referenceimage, the motion vector, and the residual data may be output via interprediction of the current region.

The inter prediction apparatus 10 according to an embodiment may performinter prediction according to blocks of each image of a video. A blockmay have a square shape, a rectangular shape, or an arbitrarygeometrical shape, and is not limited to a data unit having apredetermined size. The block according to an embodiment may be amaximum coding unit, a coding unit, a prediction unit, or atransformation unit, among coding units according to a tree structure.Video encoding and decoding methods based on coding units according to atree structure will be described later with reference to FIGS. 6 through18.

The reference image used for inter prediction of the current image mustbe decoded before the current image. The reference image for interprediction according to an embodiment may be classified into ashort-term reference image and a long-term reference image. A decodedpicture buffer stores restored images generated via motion compensationof previous images. The generated restored images may be used as thereference images for inter prediction of other images. Accordingly, atleast one short-term reference image or at least one long-term referenceimage for inter prediction of the current image may be selected fromamong the restored images stored in the decoded picture buffer. Theshort-term reference image may be an image decoded immediately orrecently before the current image according to a decoding order, whereasthe long-term reference image may be an image decoded long before thecurrent image but is selected and stored in the decoded picture bufferto be used as the reference image for inter prediction of other images.

Among the restored images stored in the decoded picture buffer, theshort-term reference images and the long-term reference images areclassified from each other. The long-term reference image is an imagereferable for inter prediction of a plurality of images, and is storedin the decoded picture buffer for a long period of time. On the otherhand, the short-term reference images each referred to for interprediction of a current image and a following image and required forevery image may be updated, and thus the short-term reference images inthe decoded picture buffer may be frequently updated. Accordingly, whennew short-term reference images are stored in the decoded picturebuffer, oldest short-term reference images among the pre-storedshort-term reference images are sequentially deleted.

The inter prediction unit 12 may perform inter prediction on the currentimage by using the long-term reference image stored in the decodedpicture buffer.

The output unit 14 may output the residual data and the motion vector ofthe current image generated via the inter prediction of the interprediction unit 12.

The output unit 14 may determine least significant bit (LSB) informationof picture order count (POC) information of the long-term referenceimage, as a long-term reference index indicating the long-term referenceimage. The output unit 14 may divide the POC information of thelong-term reference image into most significant bit (MSB) informationand the LSB information, and only output the LSB information as thelong-term reference index indicating the long-term reference image.

The inter prediction unit 12 may determine the long-term reference imageper slice. Accordingly, the output unit 14 may insert the LSBinformation of the POC information of the long-term reference image usedfor inter prediction of a current slice, as the long-term referenceindex, into a slice header. LSB information of POC information ofreference images for blocks of the current slice may be inserted intothe slice header and then transmitted.

The long-term reference image is determined according to slices, and theinter prediction may be performed according to blocks in the slice. Inother words, the inter prediction unit 12 may perform the interprediction according to blocks of the current slice by referring to thelong-term reference image. Accordingly, a reference block is determinedfrom the long-term reference image according to the blocks of thecurrent slice, and a motion vector and residual data may be determinedwith respect to the reference block according to the blocks.Accordingly, the output unit 14 may output the motion vector and theresidual data according to the blocks of the current slice.

Alternatively, the output unit 14 may divide difference informationbetween POC information of the long-term reference image and POCinformation of the current image into MSB information and LSBinformation, and output the LSB information of the differenceinformation as the long-term reference index.

The inter prediction unit 12 may perform inter prediction on the currentimage by referring to the short-term reference image. In this case,between MSB and LSB information of POC information of the short-termreference image, the output unit 14 may only output LSB information, asa short-term reference index indicating the short-term reference image.

The inter prediction apparatus 10 may include a central processor (notshown) that generally controls the inter prediction unit 12 and theoutput unit 14. Alternatively, the inter prediction unit 12 and theoutput unit 14 may each be operated by a self-processor (not shown), andthe self-processors may mutually systematically operate such that theinter prediction apparatus 10 is operated. Alternatively, the interprediction unit 12 and the output unit 14 may be controlled according toan external processor (not shown) of the inter prediction apparatus 10.

The inter prediction apparatus 10 may include one or more data storageunits (not shown) where input and output data of the inter predictionunit 12 and the output unit 14 are stored. The inter predictionapparatus 10 may include a memory control unit (not shown) forcontrolling data input and output of a data storage unit.

FIG. 1B is a flowchart illustrating an inter prediction method accordingto an embodiment of the present invention.

In operation 13, the inter prediction apparatus 10 may perform interprediction on the current image by using the long-term reference imagestored in the decoded picture buffer. In operation 15, the interprediction apparatus 10 may determine the residual data and the motionvector of the current image according to the inter prediction. Inoperation 17, the inter prediction apparatus 10 may divide the POCinformation of the long-term reference image into the MSB informationand the LSB information, and determine the LSB information of the POCinformation of the long-term reference image as the long-term referenceindex.

The residual data and the motion vector of the current image may beoutput, and the LSB information of the POC information of the long-termreference image may be output as information for indicating thelong-term reference image of the current image, as the results of theinter prediction apparatus 10 performing the inter prediction on thecurrent image by using the long-term reference image in operations 13through 17.

FIG. 2A is a block diagram of a motion compensation apparatus 20according to an embodiment of the present invention.

The motion compensation apparatus 20 includes a receiving unit 22 and amotion compensation unit 24.

The receiving unit 22 may receive encoded image data, a motion vector,and a long-term reference index.

A motion vector and residual data between a current image and areference image are generated as results of inter prediction. A processof restoring the current image by using the reference image, theresidual data, and the motion vector is motion compensation. The motioncompensation unit 24 may restore the current image by performing motioncompensation by using the residual data and the motion vector of thecurrent image received by the receiving unit 22.

The motion compensation unit 24 may restore the residual data of thecurrent image by decoding the encoded image data. When the encoded imagedata is a quantized transformation coefficient, the motion compensationunit 24 may restore the residual data of the current image by performinginverse quantization and inverse transformation on the encoded imagedata, and then perform the motion compensation on the residual data.

In detail, the motion compensation unit 24 may perform motioncompensation according to blocks of an image. A block may have a squareshape, a rectangular, shape, or an arbitrary geometrical shape, and maybe a coding unit of a tree structure of a prediction unit. As describedabove with reference to FIG. 1A, the block is not limited to a data unithaving a predetermined size.

Accordingly, the receiving unit 22 may receive the encoded image dataaccording to the blocks of the current image, and the motioncompensation unit 24 may restore the residual data and the motion vectoraccording to the blocks to perform the motion compensation using theresidual data and the motion vector according to the blocks. The currentimage may be restored by performing the motion compensation on allblocks in an image.

The motion compensation unit 24 may read LSB information of POCinformation of a long-term reference image of the current image from thelong-term reference index. The motion compensation unit 24 may determinethe POC information of the long-term reference image by composing MSBinformation of the POC information of the long-term reference image andthe LSB information read from the long-term reference index.

The motion compensation unit 24 may determine the long-term referenceimage corresponding to the determined POC information from amongreference images stored in a decoded picture buffer. The motioncompensation unit 24 may perform the motion compensation on the currentimage by using the motion vector and the residual data, based on thedetermined long-term reference image. The current image may be restoredvia the motion compensation.

The motion compensation unit 24 may predict MSB information of a secondlong-term reference image from MSB information of a first long-termreference image, from among a plurality of long-term reference imagesfor the current image stored in the decoded picture buffer.

For example, the motion compensation unit 24 may compare LSB informationof the POC information of the second long-term reference image and LSBinformation of the POC information of the first long-term referenceimage to determine whether the MSB information of the POC information ofthe second long-term reference image is higher than, lower than, orequal to the MSB information of the POC information of the firstlong-term reference image.

Accordingly, the MSB information of the POC information of the secondlong-term reference image may be predicted from the MSB information ofthe POC information of the first long-term reference image. The motioncompensation unit 24 may restore the POC information of the secondlong-term reference image by composing the LSB information of the POCinformation of the second long-term reference image, which is read fromthe received long-term reference index, and the predicted MSBinformation of the POC information of the second long-term referenceimage.

Alternatively, the motion compensation unit 24 may receive both the LSBinformation of the POC information of the long-term reference image andthe MSB information of the POC information of the long-term referenceimage, as long-term reference indexes for the current image. In thiscase, the motion compensation unit 24 may restore the POC information ofthe long-term reference image by composing the LSB and MSB informationof the POC information of the long-term reference image read from thereceived long-term reference indexes.

The motion compensation unit 24 may read LSB information of differenceinformation between the POC information of the current image and the POCinformation of the long-term reference image, from the long-termreference index. Here, the motion compensation unit 24 may restore thedifference information by composing the MSB information and the LSBinformation. The motion compensation unit 24 may determine a POC numberof the long-term reference image by subtracting or adding the restoreddifference information from or to the POC information of the currentimage.

The receiving unit 22 may parse the long-term reference index of acurrent slice from a slice header. LSB information of POC information ofreference images for blocks of the current slice may be parsed from theslice header.

Alternatively, the receiving unit 22 may receive a short-term referenceindex for inter prediction of the current image. LSB information of POCinformation of the short-term reference image for inter prediction ofthe current image may be read from the short-term reference index. Themotion compensation unit 24 may determine the POC information of theshort-term reference image by using the read LSB information of the POCinformation of the short-term reference image and MSB information of theshort-term reference image. The motion compensation unit 24 may performmotion compensation on the current image by using the short-termreference image corresponding to the determined POC information fromamong reference images stored in the decoded picture buffer.

FIG. 2B is a flowchart illustrating a motion compensation methodaccording to an embodiment of the present invention.

In operation 21, the motion compensation apparatus 20 may receiveencoded image data, a motion vector, and a long-term reference index. Inoperation 23, the motion compensation apparatus 20 may restore residualdata of the current image by decoding the encoded image data. Inoperation 25, the motion compensation apparatus 20 may read the LSBinformation of the POC information of the long-term reference image ofthe current image from the long-term reference index, and determine thePOC information of the long-term reference image by using the MSB andLSB information of the POC information of the long-term reference image.In operation 27, the motion compensation apparatus 20 may restore thecurrent image by performing motion compensation by using the motionvector and the residual data, based on the long-term reference imagecorresponding to the POC information determined in operation 25, fromamong the reference images stored in the decoded picture buffer.

In other words, the motion compensation apparatus 20 may select thelong-term reference image corresponding to the POC informationdetermined in operation 25 from among restored images stored in thedecoded picture buffer, and determine a reference region indicated bythe motion vector from the selected long-term reference image. Themotion compensation apparatus 20 may perform motion compensation fordetermining a current region by composing the residual data to thedetermined reference region. The motion compensation apparatus 20 mayrestore the current image by performing the motion compensationaccording to blocks of the current image.

According to the inter prediction apparatus 10 described above withreference to FIGS. 1A and 1B and the motion compensation apparatus 20described above with reference to FIGS. 2A and 2B, the LSB informationof the POC information of the long-term reference image may be used as along-term reference index indicating the long-term reference image fromamong the reference images used for inter prediction of an image. Thelong-term reference image may be indicated by using the POC informationwithout having to use a separate image number for the long-termreference image to identify the long-term reference image. Accordingly,no storage space for storing the separate image number for the long-termreference image may be spared. In addition, a range of indexesindicating the long-term reference images may be infinite.

FIG. 3 is a table showing the LSB information and the MSB information ofthe POC information of the long-term reference image, according to anembodiment of the present invention.

The inter prediction apparatus 10 and the motion compensation apparatus20 use the POC information of the long-term reference image to indicatethe long-term reference image. Also, the POC information is divided intothe MSB information and the LSB information. A maximum size of the LSBinformation may be pre-set. In FIG. 3, a range of the LSB information isfrom 0 to 15, and thus the maximum size of the LSB information is 16,i.e., 4 bits.

When the POC information is divided by the maximum size of the LSBinformation, a quotient may be the MSB information and a remainder maybe the LSB information.

Accordingly, while the POC information increases from 0 to 15, the MSBinformation of the POC information is 0 and the LSB informationincreases from 0 to 15. Also, while the POC information increases from16 to 31, the MSB information is 1 and the LSB information increasesfrom 0 to 15. Also, while the POC information increases from 32 to 47,the MSB information is 2 and the LSB information increases from 0 to 15.Also, when the POC information is 48, the MSB information is 3 and theLSB information is 0.

In FIG. 3, the MSB information 0, 1, 2, and 3 are all hexadecimalnumbers, and respectively denote 0, 16, 32, and 48 in decimal numbers.

When the POC information increases from 15 to 16, 31 to 32, or 47 to 48,the LSB information returns from 15 to 0. In other words, the LSBinformation may wrap around from a maximum value to a minimum valuewhenever the LSB information increases to a multiple of a maximum sizewhile sequentially increasing.

When only the LSB information is additionally determined after the MSBinformation of the POC information is pre-checked, the POC informationmay be determined by combining the MSB information and the LSBinformation.

Accordingly, the inter prediction apparatus 10 may output only the LSBinformation of the POC information of the long-term reference image soas to output the long-term reference index indicating the long-termreference image. The motion compensation apparatus 20 may read the LSBinformation of the POC information of the long-term reference image fromthe reference index received from the inter prediction apparatus 10, andrestore the POC information of the long-term reference image bycombining the LSB information to the pre-obtained MSB information.

Alternatively, the long-term reference index may denote the LSBinformation of the difference information between the POC information ofthe current image and the POC information of the reference image. Here,the motion compensation apparatus 20 may read the LSB information(DeltaPOCLtM1Lsb) of the difference information between the POCinformation of the current image and the POC information of thelong-term reference image from the long-term reference index. The motioncompensation apparatus 20 may determine the difference information(DeltaPOCLtM1) between the POC information of the current image and thePOC information of the long-term reference image by combining thepre-determined MSB information (DeltaPOCLtM1Msb) and the read LSBinformation (DeltaPOCLtM1Lsb)(DeltaPOCLtM1=DeltaPOCLtM1Msb+DeltaPOCLtM1Lsb). Also, when thedetermined difference information (DeltaPOCLtM1) is subtracted from thePOC information (PicOrderCnt) of the current image, the POC information(RefPicSetLtCurr) of the long-term reference image of the current imagemay be determined (RefPicSetLtCurr=PicOrderCnt−DeltaPOCLtM1).

The motion compensation apparatus 20 may receive the MSB information ofthe POC information of the long-term reference image from the interprediction apparatus 10. Here, the motion compensation apparatus 20 mayrestore the POC information of the long-term reference image bycombining the received MSB information and the LSB information of thePOC information of the long-term reference image.

Alternatively, the motion compensation apparatus 20 may determine MSBinformation of POC information of a current long-term reference imagebased on MSB information of POC information of a pre-determined previouslong-term reference image among a plurality of long-term referenceimages. For example, the MSB information (POCLtM1Msb) of the POCinformation of the current long-term reference image may i) higher by amaximum size (MaxPOCLtLsb) of LSB information than the MSB information(prevPOCLtM1Msb) of the POC information of the previous long-termreference image, ii) lower by the maximum size (MaxPOCLtLsb) of the LSBinformation than the MSB information (prevPOCLtM1Msb) of the POCinformation of the previous long-term reference image, or iii) equal tothe MSB information (prevPOCLtM1Msb) of the POC information of theprevious long-term reference image.

For example, the motion compensation apparatus 20 may compare the LSBinformation of the POC information of the previous long-term referenceimage and the LSB information of the POC information of the currentlong-term reference image to determine whether the MSB information ofthe POC information of the current long-term reference image is higherthan or equal to the MSB information of the POC information of theprevious long-term reference image.

According to a first condition, the LSB information (POCLtLsbM1) of thePOC information of the current long-term reference image may be smallerthan the LSB information (prevPOCLtLsbM1) of the POC information of theprevious long-term reference image, and a distance between the LSBinformation of the POC information of the current long-term referenceimage and the previous long-term reference image is higher than or equalto a half (MaxPOCLtLsb/2) of the maximum size of the LSB information.When the first condition is satisfied, the MSB information (POCLtM1Msb)of the POC information of the current long-term reference image may behigher by the maximum size (MaxPOCLtLsb) of the LSB information than theMSB information (prevPOCLtM1Msb) of the POC information of the previouslong-term reference image.

[Relational Expression according to First Condition] if( (POCLtM1Lsb <prevPOCLtM1Lsb) && ((prevPOCLtM1Lsb − POCLtM1Lsb) >= (MaxPOCLtLsb/2)) )  POCLtM1Msb = prevPOCLtM1Msb + MaxPOCLtLsb

In other words, in the first condition, it is determined that the LSBinformation is wrapped around in an increasing direction from the POCinformation of the previous long-term reference image to the POCinformation of the current long-term reference image, and thus the MSBinformation of the POC information of the current long-term referenceimage is relatively increased.

According to a second condition, the LSB information (POCLtLsbM1) of thePOC information of the current long-term reference image may be higherthan the LSB information (prevPOCLtLsbM1) of the POC information of theprevious long-term reference image, and a distance between the LSBinformation of the POC information of the current long-term referenceimage and the previous long-term reference image is higher than or equalto the half (MaxPOCLtLsb/2) of the maximum size of the LSB information.When the second condition is satisfied, the MSB information (POCLtM1Msb)of the POC information of the current long-term reference image may belower by the maximum size (MaxPOCLtLsb) of the LSB information than theMSB information (prevPOCLtM1Msb) of the POC information of the previouslong-term reference image.

[Relational Expression according to Second Condition] if( (POCLtM1Lsb >prevPOCLtM1Lsb) && ((prevPOCLtM1Lsb − POCLtM1Lsb) >= (MaxPOCLtLsb/2)) )  POCLtM1Msb = prevPOCLtM1Msb − MaxPOCLtLsb

In other words, in the second condition, it is determined that the LSBinformation is wrapped around in a decreasing direction from the POCinformation of the previous long-term reference image to the POCinformation of the current long-term reference image, and thus the MSBinformation of the POC information of the current long-term referenceimage is relatively decreased.

A third condition is applied when the first and second conditions cannotbe applied. In the third condition, the MSB information (POCLtM1Msb) ofthe POC information of the current long-term reference image may beequal to the MSB information (prevPOCLtM1Msb) of the POC information ofthe previous long-term reference image.

[Relational Expression according to Third Condition]

POCLtM1Msb=prevPOCLtM1Msb

The MSB information (POCLtM1Msb) of the POC information of the currentlong-term reference image is determined by considering all of the firstthrough third conditions, and the POC information (POCLtM1) of thecurrent long-term reference image may be determined by combining the LSBinformation (POCLtM1Lsb) of the POC information of the current long-termreference image, which is read form the long-term reference index, tothe determined MSB information (POCLtM1Msb).(POCLtM1=POCLtM1Msb+POCLtM1Lsb)

Even when the LSB information of the difference information between POCinformation of the current image and the long-term reference imagedescribed above is used as the long-term reference index, it may bedetermined whether LSB information of difference information between POCinformation of the current image and the current long-term referenceimage is higher, lower, or equal based on LSB information of thedifference information between POC information of the current image andthe pre-determined previous long-term reference image.

FIG. 4 is a block diagram of a video encoding apparatus 40 that performsinter prediction, according to an embodiment of the present invention.

The video encoding apparatus 40 includes a decoded picture buffer 42, aninter prediction unit 44, a transformation quantization unit 46, and anentropy encoding unit 48.

The decoded picture buffer 42 stores previously restored images.Reference images for inter prediction of an image may be determined fromamong the restored images stored in the decoded picture buffer 42. Theinter prediction unit 44 may generate residual data by performing interprediction on a current image by using a long-term reference imageselected from among the restored images stored in the decoded picturebuffer 42. The inter prediction unit 44 may perform the same operationsas the inter prediction apparatus 10 described above.

The transformation quantization unit 46 may generate a quantizedtransformation coefficient by performing transformation and quantizationon the residual data generated by the inter prediction unit 44. Theentropy encoding unit 48 may perform entropy encoding on symbolsincluding the quantized transformation coefficient and a motion vector.

Accordingly, the video encoding apparatus 40 may perform interprediction according to blocks of images of a video, generate aquantized transformation coefficient according to the blocks byperforming transformation and quantization on residual data generatedaccording to blocks via inter prediction, and output a bitstream byperforming entropy encoding on the quantized transformation coefficient,thereby encoding the video.

The entropy encoding unit 48 may output the motion vector determined viathe inter prediction, together with the quantized transformationcoefficient. Accordingly, the entropy encoding may be performed onsymbols including the quantized transformation coefficient and themotion vector.

Also, the long-term reference index determined by the inter predictionunit 44 may be output as the symbol. The long-term reference index maybe the LSB information of the POC information of the long-term referenceimage. Accordingly, the entropy encoding unit 48 may perform the entropyencoding on the symbol including the quantized transformationcoefficient, the motion vector, and the long-term reference index. Theentropy encoding unit 48 may output the bitstream generated according tothe entropy encoding.

Also, the video encoding apparatus 40 may generate the restored image ofthe current image by performing motion compensation using the residualdata and the motion vector of the current image by referring to therestored images stored in the decoded picture buffer 42, in order togenerate the reference image for inter prediction of other images.Accordingly, the video encoding apparatus 40 may perform operations ofthe motion compensation apparatus 20 to perform motion compensation.

In other words, the video encoding apparatus 40 may read the LSBinformation of the POC information from the long-term reference indexand restore the POC information of the long-term reference image byusing the read LSB information, so as to select the long-term referenceimage for motion compensation. The video encoding apparatus 40 mayselect the long-term reference image corresponding to the restored POCinformation from among the restored images stored in the decoded picturebuffer 42, and perform the motion compensation using the residual dataand the motion vector of the current image based on the selectedlong-term reference image.

In order to output a video encoding result, the video encoding apparatus40 may operate in cooperation with a video encoding processor installedtherein or an external video encoding processor so as to perform videoencoding operations including intra prediction, inter prediction,transformation, and quantization. The video encoding operations may beperformed not only when the video encoding apparatus 40 includes aseparate internal video encoding processor, but also when the videoencoding apparatus 40 or a central processing apparatus or graphicprocessing apparatus for controlling the video encoding apparatus 40includes a video encoding processing module.

FIG. 5 is a block diagram of a video decoding apparatus 50 that performsmotion compensation, according to an embodiment of the presentinvention.

The video decoding apparatus 50 may include a receiving unit 52, aninverse quantization and inverse transformation unit 54, a decodedpicture buffer 56, a motion compensation unit 58, and an in-loopfiltering unit 59.

The receiving unit 52 may receive a video stream and perform entropydecoding on the received video stream to parse encoded image data.

The inverse quantization and inverse transformation unit 54 may restoreresidual data by performing inverse quantization and inversetransformation on the encoded image data parsed by the receiving unit52.

The receiving unit 52 may parse a motion vector from the vide stream.The decoded picture buffer 56 may store the previously restored imagesthat may be used as a reference image for motion compensation of otherimages. The motion compensation unit 58 may perform motion compensationusing the motion vector and the residual data based on the referenceimages stored in the decoded picture buffer 56.

The in-loop filtering unit 59 may perform deblocking filtering on therestored image restored and output by the motion compensation unit 58.The in-loop filtering unit 59 may output a final restored image. Also,an output image of the in-loop filtering unit 59 may be stored in thedecoded picture buffer 56 and used as a reference image for motioncompensation of a following image.

The video decoding apparatus 50 may restore a video by performingdecoding according to blocks of images of the video. The receiving unit52 may parse the encoded image data and the motion vector according tothe blocks, and the inverse quantization and inverse transformation unit54 may restore the residual data according to the blocks by performinginverse quantization and inverse transformation according to the blocks.The motion compensation unit 58 may determine a reference blockindicated by the motion vector from among the reference images accordingto the blocks, and generate restored blocks by composing the referenceblock and the residual data.

The receiving unit 52 may parse the long-term reference index from thevideo stream. The motion compensation unit 58 may perform the sameoperations as the motion compensation apparatus 20 described above. Themotion compensation unit 58 may read the LSB information of the POCinformation of the long-term reference image of the current image fromthe long-term reference index, and determine the POC information of thelong-term reference image by using the MSB and LSB information of thelong-term reference image. The motion compensation unit 58 may performmotion compensation using the motion vector and the residual data basedon the long-term reference image corresponding to the POC informationfrom among the restored images stored in the decoded picture buffer 56.In other words, the motion compensation unit 58 may determine thereference block indicated by the motion vector from among the long-termreference image, and restore the current block by composing thereference block and the residual data.

In order to output a video decoding result, the video decoding apparatus50 may operate in cooperation with a video decoding processor installedtherein or an external video decoding processor to perform videodecoding operations including inverse quantization, inversetransformation, intra prediction, and motion compensation. The videodecoding operations may be performed not only when the video decodingapparatus 50 includes a separate internal video decoding processor, butalso when the video decoding apparatus 50 or a central processingapparatus or graphic processing apparatus for controlling the videodecoding apparatus 50 includes a video decoding processing module.

As described above, the inter prediction apparatus 10 may spilt blocksof video data into coding units having a tree structure, and predictionunits for inter prediction of coding units may be used. Hereinafter, avideo encoding method, a video encoding apparatus, a video decodingmethod, and a video decoding apparatus based on coding units having atree structure and transformation units will be described with referenceto FIGS. 6 through 18.

FIG. 6 is a block diagram of a video encoding apparatus 100 based oncoding units according to a tree structure, according to an embodimentof the present invention.

The video encoding apparatus 100 involving video prediction based oncoding units according to a tree structure includes a maximum codingunit splitter 110, a coding unit determiner 120, and an output unit 130.

The maximum coding unit splitter 110 may split a current picture basedon a maximum coding unit that is a coding unit having a maximum size fora current picture of an image. If the current picture is larger than themaximum coding unit, image data of the current picture may be split intothe at least one maximum coding unit. The maximum coding unit accordingto an embodiment of the present invention may be a data unit having asize of 32×32, 64×64, 128×128, 256×256, etc., wherein a shape of thedata unit is a square having a width and length in squares of 2. Theimage data may be output to the coding unit determiner 120 according tothe at least one maximum coding unit.

A coding unit according to an embodiment of the present invention may becharacterized by a maximum size and a depth. The depth denotes thenumber of times the coding unit is spatially split from the maximumcoding unit, and as the depth deepens, deeper coding units according todepths may be split from the maximum coding unit to a minimum codingunit. A depth of the maximum coding unit is an uppermost depth and adepth of the minimum coding unit is a lowermost depth. Since a size of acoding unit corresponding to each depth decreases as the depth of themaximum coding unit deepens, a coding unit corresponding to an upperdepth may include a plurality of coding units corresponding to lowerdepths.

As described above, the image data of the current picture is split intothe maximum coding units according to a maximum size of the coding unit,and each of the maximum coding units may include deeper coding unitsthat are split according to depths. Since the maximum coding unitaccording to an embodiment of the present invention is split accordingto depths, the image data of a spatial domain included in the maximumcoding unit may be hierarchically classified according to depths.

A maximum depth and a maximum size of a coding unit, which limit thetotal number of times a height and a width of the maximum coding unitare hierarchically split, may be predetermined.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the maximum coding unit according todepths, and determines a depth to output a finally encoded image dataaccording to the at least one split region. In other words, the codingunit determiner 120 determines a coded depth by encoding the image datain the deeper coding units according to depths, according to the maximumcoding unit of the current picture, and selecting a depth having theleast encoding error. The determined coded depth and the encoded imagedata according to the determined coded depth are output to the outputunit 130.

The image data in the maximum coding unit is encoded based on the deepercoding units corresponding to at least one depth equal to or below themaximum depth, and results of encoding the image data are compared basedon each of the deeper coding units. A depth having the least encodingerror may be selected after comparing encoding errors of the deepercoding units. At least one coded depth may be selected for each maximumcoding unit.

The size of the maximum coding unit is split as a coding unit ishierarchically split according to depths, and as the number of codingunits increases. Also, even if coding units correspond to the same depthin one maximum coding unit, it is determined whether to split each ofthe coding units corresponding to the same depth to a lower depth bymeasuring an encoding error of the image data of the each coding unit,separately. Accordingly, even when image data is included in one maximumcoding unit, the encoding errors may differ according to regions in theone maximum coding unit, and thus the coded depths may differ accordingto regions in the image data. Thus, one or more coded depths may bedetermined in one maximum coding unit, and the image data of the maximumcoding unit may be divided according to coding units of at least onecoded depth.

Accordingly, the coding unit determiner 120 may determine coding unitshaving a tree structure included in the maximum coding unit. The ‘codingunits having a tree structure’ according to an embodiment of the presentinvention include coding units corresponding to a depth determined to bethe coded depth, from among all deeper coding units included in themaximum coding unit. A coding unit of a coded depth may behierarchically determined according to depths in the same region of themaximum coding unit, and may be independently determined in differentregions. Similarly, a coded depth in a current region may beindependently determined from a coded depth in another region.

A maximum depth according to an embodiment of the present invention isan index related to the number of splitting times from a maximum codingunit to a minimum coding unit. A first maximum depth according to anembodiment of the present invention may denote the total number ofsplitting times from the maximum coding unit to the minimum coding unit.A second maximum depth according to an embodiment of the presentinvention may denote the total number of depth levels from the maximumcoding unit to the minimum coding unit. For example, when a depth of themaximum coding unit is 0, a depth of a coding unit, in which the maximumcoding unit is split once, may be set to 1, and a depth of a codingunit, in which the maximum coding unit is split twice, may be set to 2.Here, if the minimum coding unit is a coding unit in which the maximumcoding unit is split four times, 5 depth levels of depths 0, 1, 2, 3,and 4 exist, and thus the first maximum depth may be set to 4, and thesecond maximum depth may be set to 5.

Prediction encoding and transformation may be performed according to themaximum coding unit. The prediction encoding and the transformation arealso performed based on the deeper coding units according to a depthequal to or depths less than the maximum depth, according to the maximumcoding unit.

Since the number of deeper coding units increases whenever the maximumcoding unit is split according to depths, encoding, including theprediction encoding and the transformation, is performed on all of thedeeper coding units generated as the depth deepens. For convenience ofdescription, the prediction encoding and the transformation will now bedescribed based on a coding unit of a current depth, in a maximum codingunit.

The video encoding apparatus 100 may variously select a size or shape ofa data unit for encoding the image data. In order to encode the imagedata, operations, such as prediction encoding, transformation, andentropy encoding, are performed, and at this time, the same data unitmay be used for all operations or different data units may be used foreach operation.

For example, the video encoding apparatus 100 may select not only acoding unit for encoding the image data, but also a data unit differentfrom the coding unit so as to perform the prediction encoding on theimage data in the coding unit.

In order to perform prediction encoding in the maximum coding unit, theprediction encoding may be performed based on a coding unitcorresponding to a coded depth, i.e., based on a coding unit that is nolonger split to coding units corresponding to a lower depth.Hereinafter, the coding unit that is no longer split and becomes a basisunit for prediction encoding will now be referred to as a ‘predictionunit’. A partition obtained by splitting the prediction unit may includea prediction unit or a data unit obtained by splitting at least one of aheight and a width of the prediction unit. A partition is a data unitwhere a prediction unit of a coding unit is split, and a prediction unitmay be a partition having the same size as a coding unit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split and becomes a prediction unit of 2N×2N, and a size ofa partition may be 2N×2N, 2N×N, N×2N, or N×N. Examples of a partitiontype include symmetrical partitions that are obtained by symmetricallysplitting a height or width of the prediction unit, partitions obtainedby asymmetrically splitting the height or width of the prediction unit,such as 1:n or n:1, partitions that are obtained by geometricallysplitting the prediction unit, and partitions having arbitrary shapes.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, the intra mode or theinter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, orN×N. Also, the skip mode may be performed only on the partition of2N×2N. The encoding is independently performed on one prediction unit ina coding unit, thereby selecting a prediction mode having a leastencoding error.

The video encoding apparatus 100 may also perform the transformation onthe image data in a coding unit based not only on the coding unit forencoding the image data, but also based on a data unit that is differentfrom the coding unit. In order to perform the transformation in thecoding unit, the transformation may be performed based on a data unithaving a size smaller than or equal to the coding unit. For example, thedata unit for the transformation may include a data unit for an intramode and a data unit for an inter mode.

The transformation unit in the coding unit may be recursively split intosmaller sized regions in the similar manner as the coding unit accordingto the tree structure. Thus, residual data in the coding unit may bedivided according to the transformation unit having the tree structureaccording to transformation depths.

A transformation depth indicating the number of splitting times to reachthe transformation unit by splitting the height and width of the codingunit may also be set in the transformation unit. For example, in acurrent coding unit of 2N×2N, a transformation depth may be 0 when thesize of a transformation unit is 2N×2N, may be 1 when the size of thetransformation unit is N×N, and may be 2 when the size of thetransformation unit is N/2×N/2. In other words, the transformation unithaving the tree structure may be set according to the transformationdepths.

Encoding information according to coding units corresponding to a codeddepth requires not only information about the coded depth, but alsoabout information related to prediction encoding and transformation.Accordingly, the coding unit determiner 120 not only determines a codeddepth having a least encoding error, but also determines a partitiontype in a prediction unit, a prediction mode according to predictionunits, and a size of a transformation unit for transformation.

Coding units according to a tree structure in a maximum coding unit andmethods of determining a prediction unit/partition, and a transformationunit, according to embodiments of the present invention, will bedescribed in detail later with reference to FIGS. 8 through 18.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using Rate-Distortion Optimizationbased on Lagrangian multipliers.

The output unit 130 outputs the image data of the maximum coding unit,which is encoded based on the at least one coded depth determined by thecoding unit determiner 120, and information about the encoding modeaccording to the coded depth, in bitstreams.

The encoded image data may be obtained by encoding residual data of animage.

The information about the encoding mode according to coded depth mayinclude information about the coded depth, about the partition type inthe prediction unit, the prediction mode, and the size of thetransformation unit.

The information about the coded depth may be defined by using splitinformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the coded depth,image data in the current coding unit is encoded and output, and thusthe split information may be defined not to split the current codingunit to a lower depth. Alternatively, if the current depth of thecurrent coding unit is not the coded depth, the encoding is performed onthe coding unit of the lower depth, and thus the split information maybe defined to split the current coding unit to obtain the coding unitsof the lower depth.

If the current depth is not the coded depth, encoding is performed onthe coding unit that is split into the coding unit of the lower depth.Since at least one coding unit of the lower depth exists in one codingunit of the current depth, the encoding is repeatedly performed on eachcoding unit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for onemaximum coding unit, and information about at least one encoding mode isdetermined for a coding unit of a coded depth, information about atleast one encoding mode may be determined for one maximum coding unit.Also, a coded depth of the image data of the maximum coding unit may bedifferent according to locations since the image data is hierarchicallysplit according to depths, and thus information about the coded depthand the encoding mode may be set for the image data.

Accordingly, the output unit 130 may assign encoding information about acorresponding coded depth and an encoding mode to at least one of thecoding unit, the prediction unit, and a minimum unit included in themaximum coding unit.

The minimum unit according to an embodiment of the present invention isa square data unit obtained by splitting the minimum coding unitconstituting the lowermost depth by 4. Alternatively, the minimum unitaccording to an embodiment may be a maximum square data unit that may beincluded in all of the coding units, prediction units, partition units,and transformation units included in the maximum coding unit.

For example, the encoding information output by the output unit 130 maybe classified into encoding information according to deeper codingunits, and encoding information according to prediction units. Theencoding information according to the deeper coding units may includethe information about the prediction mode and about the size of thepartitions. The encoding information according to the prediction unitsmay include information about an estimated direction of an inter mode,about a reference image index of the inter mode, about a motion vector,about a chroma component of an intra mode, and about an interpolationmethod of the intra mode.

Information about a maximum size of the coding unit defined according topictures, slices, or GOPs, and information about a maximum depth may beinserted into a header of a bitstream, a sequence parameter set, or apicture parameter set.

Information about a maximum size of the transformation unit permittedwith respect to a current video, and information about a minimum size ofthe transformation unit may also be output through a header of abitstream, a sequence parameter set, or a picture parameter set. Theoutput unit 130 may encode and output reference information related toprediction, prediction information, and slice type information, whichare described above with reference to FIGS. 1 through 6.

In the video encoding apparatus 100, the deeper coding unit may be acoding unit obtained by dividing a height or width of a coding unit ofan upper depth, which is one layer above, by two. In other words, whenthe size of the coding unit of the current depth is 2N×2N, the size ofthe coding unit of the lower depth is N×N. Also, the coding unit withthe current depth having a size of 2N×2N may include a maximum of 4 ofthe coding units with the lower depth.

Accordingly, the video encoding apparatus 100 may form the coding unitshaving the tree structure by determining coding units having an optimumshape and an optimum size for each maximum coding unit, based on thesize of the maximum coding unit and the maximum depth determinedconsidering characteristics of the current picture. Also, since encodingmay be performed on each maximum coding unit by using any one of variousprediction modes and transformations, an optimum encoding mode may bedetermined considering characteristics of the coding unit of variousimage sizes.

Thus, if an image having a high resolution or a large data amount isencoded in a conventional macroblock, the number of macroblocks perpicture excessively increases. Accordingly, the number of pieces ofcompressed information generated for each macroblock increases, and thusit is difficult to transmit the compressed information and datacompression efficiency decreases. However, by using the video encodingapparatus 100, image compression efficiency may be increased since acoding unit is adjusted while considering characteristics of an imagewhile increasing a maximum size of a coding unit while considering asize of the image.

The video encoding apparatus 100 of FIG. 6 may perform operations of theinter prediction apparatus 10 of FIG. 1A or the video encoding apparatus40 of FIG. 4.

The coding unit determiner 120 and the output unit 130 may performoperations of the inter prediction apparatus 10 or the inter predictionunit 44. A prediction unit for inter prediction may be determinedaccording to coding units having a tree structure for each maximumcoding unit, and inter prediction may be performed per prediction unit.

Specifically, when the long-term reference image is used for interprediction of a current prediction unit in an inter mode, the POCinformation of the long-term reference image may be used as thelong-term reference index for identifying the long-term reference imagesstored in the decoded picture buffer. The output unit 130 may output theLSB information of the POC information of the long-term reference image,as the reference index. Also, the reference index indicating thelong-term reference image to be referred to in the current slice may bestored in the slice header. Accordingly, the output unit 130 maytransmit the LSB information of the POC information of the long-termreference image as the reference index through the slice header.

Also, the coding unit determiner 120 may perform motion compensation fora current image by referring to a previous restored image stored in thedecoded picture buffer so as to generate the reference image for interprediction of other images. Accordingly, the coding unit determiner 120may perform operations of the video decoding apparatus 50 described withreference to FIG. 5.

In other words, the coding unit determiner 120 may also read the LSBinformation of the POC information from the long-term reference indexand restore the POC information of the long-term reference image byusing the read LSB information so as to select the long-term referenceimage for motion compensation. The coding unit determiner 120 may selectthe long-term reference image corresponding to the restored POCinformation from among restored images stored in the decoded picturebuffer, and perform motion compensation using the motion vector and theresidual data based on the selected long-term reference image.

Since the coding unit determiner 120 performs motion compensationaccording to prediction units, the coding unit determiner 120 maydetermine a reference prediction unit indicated by a motion vector of acurrent prediction unit from the selected long-term reference image, andrestore the current prediction unit by composing residual data of thecurrent prediction unit and the determined reference prediction unit. Acoding unit may be restored by restoring prediction units, a maximumcoding unit may be restored by restoring coding units, and an image maybe restored by restoring maximum coding units.

FIG. 7 is a block diagram of a video decoding apparatus 200 based oncoding units having a tree structure, according to an embodiment of thepresent invention.

The video decoding apparatus 200 that involves video prediction based oncoding units having a tree structure includes a receiver 210, an imagedata and encoding information extractor 220, and an image data decoder230.

Definitions of various terms, such as a coding unit, a depth, aprediction unit, a transformation unit, and information about variousencoding modes, for decoding operations of the video decoding apparatus200 are identical to those described with reference to FIG. 6 and thevideo encoding apparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, wherein thecoding units have a tree structure according to each maximum codingunit, and outputs the extracted image data to the image data decoder230. The image data and encoding information extractor 220 may extractinformation about a maximum size of a coding unit of a current picture,from a header about the current picture, a sequence parameter set, or apicture parameter set.

Also, the image data and encoding information extractor 220 extractsinformation about a coded depth and an encoding mode for the codingunits having a tree structure according to each maximum coding unit,from the parsed bitstream. The extracted information about the codeddepth and the encoding mode is output to the image data decoder 230. Inother words, the image data in a bit stream is split into the maximumcoding unit so that the image data decoder 230 decodes the image datafor each maximum coding unit.

The information about the coded depth and the encoding mode according tothe maximum coding unit may be set for information about at least onecoding unit corresponding to the coded depth, and information about anencoding mode may include information about a partition type of acorresponding coding unit corresponding to the coded depth, about aprediction mode, and a size of a transformation unit. Also, splittinginformation according to depths may be extracted as the informationabout the coded depth.

The information about the coded depth and the encoding mode according toeach maximum coding unit extracted by the image data and encodinginformation extractor 220 is information about a coded depth and anencoding mode determined to generate a minimum encoding error when anencoder, such as the video encoding apparatus 100, repeatedly performsencoding for each deeper coding unit according to depths according toeach maximum coding unit. Accordingly, the video decoding apparatus 200may restore an image by decoding the image data according to a codeddepth and an encoding mode that generates the minimum encoding error.

Since encoding information about the coded depth and the encoding modemay be assigned to a predetermined data unit from among a correspondingcoding unit, a prediction unit, and a minimum unit, the image data andencoding information extractor 220 may extract the information about thecoded depth and the encoding mode according to the predetermined dataunits. If information about a coded depth and encoding mode of acorresponding maximum coding unit is recorded according to predetermineddata units, the predetermined data units to which the same informationabout the coded depth and the encoding mode is assigned may be inferredto be the data units included in the same maximum coding unit.

The image data decoder 230 restores the current picture by decoding theimage data in each maximum coding unit based on the information aboutthe coded depth and the encoding mode according to the maximum codingunits. In other words, the image data decoder 230 may decode the encodedimage data based on the extracted information about the partition type,the prediction mode, and the transformation unit for each coding unitfrom among the coding units having the tree structure included in eachmaximum coding unit. A decoding process may include a predictionincluding intra prediction and motion compensation, and an inversetransformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition type and theprediction mode of the prediction unit of the coding unit according tocoded depths.

In addition, the image data decoder 230 may read information about atransformation unit according to a tree structure for each coding unitso as to perform inverse transformation based on transformation unitsfor each coding unit, for inverse transformation for each maximum codingunit. Via the inverse transformation, a pixel value of a spatial regionof the coding unit may be restored.

The image data decoder 230 may determine a coded depth of a currentmaximum coding unit by using split information according to depths. Ifthe split information indicates that image data is no longer split inthe current depth, the current depth is a coded depth. Accordingly, theimage data decoder 230 may decode encoded data in the current maximumcoding unit by using the information about the partition type of theprediction unit, the prediction mode, and the size of the transformationunit for each coding unit corresponding to the coded depth.

In other words, data units containing the encoding information includingthe same split information may be gathered by observing the encodinginformation set assigned for the predetermined data unit from among thecoding unit, the prediction unit, and the minimum unit, and the gathereddata units may be considered to be one data unit to be decoded by theimage data decoder 230 in the same encoding mode. As such, the currentcoding unit may be decoded by obtaining the information about theencoding mode for each coding unit.

Also, the image data decoder 230 of the video decoding apparatus 200 ofFIG. 7 may perform operations of the motion compensation apparatus 20 ofFIG. 2A or the motion compensation unit 58 of FIG. 5.

The image data and encoding information extractor 220 may parse thelong-term reference index from the received bitstream. The long-termreference index may be parsed from the slice header.

The image data decoder 230 may determine the prediction unit for interprediction and perform inter prediction for each prediction unit,according to coding units having a tree structure, for each maximumcoding unit.

Specifically, the image data decoder 230 may read the LSB information ofthe POC information of the long-term reference image from the long-termreference index. The image data decoder 230 may restore the POCinformation of the long-term reference image by combining the read LSBinformation and the pre-determined MSB information of the POCinformation of the long-term reference image.

Since the image data decoder 230 performs motion compensation accordingto prediction units, the image data decoder 230 may determine thereference prediction unit indicated by the motion vector of the currentprediction unit from the long-term reference image, and restore thecurrent prediction unit by composing the residual data of the currentprediction unit to the reference prediction unit. The coding unit may berestored by restoring the prediction units, the maximum coding unit maybe restored by restoring the coding units, and the image may be restoredby restoring the maximum coding units.

Thus, the video decoding apparatus 200 may obtain information about atleast one coding unit that generates the minimum encoding error whenencoding is recursively performed for each maximum coding unit, and mayuse the information to decode the current picture. In other words, thecoding units having the tree structure determined to be the optimumcoding units in each maximum coding unit may be decoded.

Accordingly, even if image data has high resolution and a large amountof data, the image data may be efficiently decoded and restored by usinga size of a coding unit and an encoding mode, which are adaptivelydetermined according to characteristics of the image data, by usinginformation about an optimum encoding mode received from an encoder.

FIG. 8 is a diagram for describing a concept of coding units accordingto an embodiment of the present invention.

A size of a coding unit may be expressed by width×height, and may be64×64, 32×32, 16×16, and 8×8. A coding unit of 64×64 may be split intopartitions of 64×64, 64×32, 32×64, or 32×32, and a coding unit of 32×32may be split into partitions of 32×32, 32×16, 16×32, or 16×16, a codingunit of 16×16 may be split into partitions of 16×16, 16×8, 8×16, or 8×8,and a coding unit of 8×8 may be split into partitions of 8×8, 8×4, 4×8,or 4×4.

In video data 310, a resolution is 1920×1080, a maximum size of a codingunit is 64, and a maximum depth is 2. In video data 320, a resolution is1920×1080, a maximum size of a coding unit is 64, and a maximum depth is3. In video data 330, a resolution is 352×288, a maximum size of acoding unit is 16, and a maximum depth is 1. The maximum depth shown inFIG. 8 denotes a total number of splits from a maximum coding unit to aminimum coding unit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large so as to not only increase encoding efficiencybut also to accurately reflect characteristics of an image. Accordingly,the maximum size of the coding unit of the video data 310 and 320 havinga higher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe vide data 310 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32 and 16 sincedepths are deepened to two layers by splitting the maximum coding unittwice. Since the maximum depth of the video data 330 is 1, coding units335 of the video data 330 may include a maximum coding unit having along axis size of 16, and coding units having a long axis size of 8since depths are deepened to one layer by splitting the maximum codingunit once.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32, 16, and 8since the depths are deepened to 3 layers by splitting the maximumcoding unit three times. As a depth deepens, detailed information may beprecisely expressed.

FIG. 9 is a block diagram of an image encoder 400 based on coding units,according to an embodiment of the present invention.

The image encoder 400 performs operations of the coding unit determiner120 of the video encoding apparatus 100 to encode image data. In otherwords, an intra predictor 410 performs intra prediction on coding unitsin an intra mode, from among a current frame 405, and a motion estimator420 and a motion compensator 425 respectively perform inter estimationand motion compensation on coding units in an inter mode from among thecurrent frame 405 by using the current frame 405, and a reference frame495.

Data output from the intra predictor 410, the motion estimator 420, andthe motion compensator 425 is output as a quantized transformationcoefficient through a transformer 430 and a quantizer 440. The quantizedtransformation coefficient is restored as data in a spatial domainthrough an inverse quantizer 460 and an inverse transformer 470, and therestored data in the spatial domain is output as the reference frame 495after being post-processed through a deblocking unit 480 and a loopfiltering unit 490. The quantized transformation coefficient may beoutput as a bitstream 455 through an entropy encoder 450.

In order for the image encoder 400 to be applied in the video encodingapparatus 100, all elements of the image encoder 400, i.e., the intrapredictor 410, the motion estimator 420, the motion compensator 425, thetransformer 430, the quantizer 440, the entropy encoder 450, the inversequantizer 460, the inverse transformer 470, the deblocking unit 480, andthe loop filtering unit 490 perform operations based on each coding unitamong coding units having a tree structure while considering the maximumdepth of each maximum coding unit.

Specifically, the intra predictor 410, the motion estimator 420, and themotion compensator 425 determines partitions and a prediction mode ofeach coding unit from among the coding units having a tree structurewhile considering the maximum size and the maximum depth of a currentmaximum coding unit, and the transformer 430 determines the size of thetransformation unit in each coding unit from among the coding unitshaving a tree structure.

Specifically, when the motion estimator 420 performs the interprediction using the long-term reference frame, the POC information ofthe long-term reference frame may be output as the long-term referenceindex. The entropy encoder 450 may encode and output the LSB informationof the POC information of the long-term reference frame, as thelong-term reference index. The LSB information of the POC information ofthe long-term reference frames for the prediction units of the currentslice may be included in the slice header and then transmitted.

The motion compensator 425 may also determine the POC information of thelong-term reference frame by using the LSB information of the POCinformation read from the long-term reference index. The motioncompensation unit 425 may select the long-term reference framecorresponding to the restored POC information from the reference framesstored in the decoded picture buffer, and perform motion compensationusing the residual data and the motion vector of the current frame basedon the selected long-term reference frame.

FIG. 10 is a block diagram of an image decoder 500 based on codingunits, according to an embodiment of the present invention.

A parser 510 parses encoded image data to be decoded and informationabout encoding required for decoding from a bitstream 505. The encodedimage data is output as inverse quantized data through an entropydecoder 520 and an inverse quantizer 530, and the inverse quantized datais restored to image data in a spatial domain through an inversetransformer 540.

An intra predictor 550 performs intra prediction on coding units in anintra mode with respect to the image data in the spatial domain, and amotion compensator 560 performs motion compensation on coding units inan inter mode by using a reference frame 585.

The image data in the spatial domain, which passed through the intrapredictor 550 and the motion compensator 560, may be output as arestored frame 595 after being post-processed through a deblocking unit570 and a loop filtering unit 580. Also, the image data that ispost-processed through the deblocking unit 570 and the loop filteringunit 580 may be output as the reference frame 585.

In order to decode the image data in the image data decoder 230 of thevideo decoding apparatus 200, the image decoder 500 may performoperations that are performed after the parser 510.

In order for the image decoder 500 to be applied in the video decodingapparatus 200, all elements of the image decoder 500, i.e., the parser510, the entropy decoder 520, the inverse quantizer 530, the inversetransformer 540, the intra predictor 550, the motion compensator 560,the deblocking unit 570, and the loop filtering unit 580 performoperations based on coding units having a tree structure for eachmaximum coding unit.

Specifically, the intra prediction 550 and the motion compensator 560perform operations based on partitions and a prediction mode for each ofthe coding units having a tree structure, and the inverse transformer540 perform operations based on a size of a transformation unit for eachcoding unit.

Specifically, the parser 510 may parse the long-term reference indexfrom the bitstream 505. The LSB information of POC information of thelong-term reference images for the prediction units of the current slicemay be parsed from the slice header. The motion compensator 560 mayrestore the POC information of the current long-term reference image bycombining the LSB and MSB information of the POC information of thecurrent long-term reference image, and determine the current long-termreference image corresponding to the restored POC information from amongthe long-term reference images stored in the decoded picture buffer.

The motion compensator 560 may determine the reference prediction unitindicated by the motion vector for the current prediction unit from thecurrent long-term reference image, and restore the current predictionunit by combining the reference prediction unit and the residual data ofthe current prediction unit.

FIG. 11 is a diagram illustrating deeper coding units according todepths, and partitions, according to an embodiment of the presentinvention.

The video encoding apparatus 100 and the video decoding apparatus 200use hierarchical coding units so as to consider characteristics of animage. A maximum height, a maximum width, and a maximum depth of codingunits may be adaptively determined according to the characteristics ofthe image, or may be differently set by a user. Sizes of deeper codingunits according to depths may be determined according to thepredetermined maximum size of the coding unit.

In a hierarchical structure 600 of coding units, according to anembodiment of the present invention, the maximum height and the maximumwidth of the coding units are each 64, and the maximum depth is 4. Inthis case, the maximum depth refers to a total number of times thecoding unit is split from the maximum coding unit to the minimum codingunit. Since a depth deepens along a vertical axis of the hierarchicalstructure 600, a height and a width of the deeper coding unit are eachsplit. Also, a prediction unit and partitions, which are bases forprediction encoding of each deeper coding unit, are shown along ahorizontal axis of the hierarchical structure 600.

In other words, a coding unit 610 is a maximum coding unit in thehierarchical structure 600, wherein a depth is 0 and a size, i.e., aheight by width, is 64×64. The depth deepens along the vertical axis,and a coding unit 620 having a size of 32×32 and a depth of 1, a codingunit 630 having a size of 16×16 and a depth of 2, and a coding unit 640having a size of 8×8 and a depth of 3. The coding unit 640 having a sizeof 8×8 and a depth of 3 is a minimum coding unit.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having a size of 64×64 and a depth of 0 is aprediction unit, the prediction unit may be split into partitionsinclude in the encoding unit 610, i.e. a partition 610 having a size of64×64, partitions 612 having the size of 64×32, partitions 614 havingthe size of 32×64, or partitions 616 having the size of 32×32.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e. a partition 620 having a size of 32×32, partitions622 having a size of 32×16, partitions 624 having a size of 16×32, andpartitions 626 having a size of 16×16.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e. a partition having a size of 16×16 included in thecoding unit 630, partitions 632 having a size of 16×8, partitions 634having a size of 8×16, and partitions 636 having a size of 8×8.

Similarly, a prediction unit of the coding unit 640 having the size of8×8 and the depth of 3 may be split into partitions included in thecoding unit 640, i.e. a partition having a size of 8×8 included in thecoding unit 640, partitions 642 having a size of 8×4, partitions 644having a size of 4×8, and partitions 646 having a size of 4×4.

In order to determine the at least one coded depth of the coding unitsconstituting the maximum coding unit 610, the coding unit determiner 120of the video encoding apparatus 100 performs encoding for coding unitscorresponding to each depth included in the maximum coding unit 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth deepens. Forexample, four coding units corresponding to a depth of 2 are required tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 are each encoded.

In order to perform encoding for a current depth from among the depths,a least encoding error may be selected for the current depth byperforming encoding for each prediction unit in the coding unitscorresponding to the current depth, along the horizontal axis of thehierarchical structure 600. Alternatively, the minimum encoding errormay be searched for by comparing the least encoding errors according todepths, by performing encoding for each depth as the depth deepens alongthe vertical axis of the hierarchical structure 600. A depth and apartition having the minimum encoding error in the coding unit 610 maybe selected as the coded depth and a partition type of the coding unit610.

FIG. 12 is a diagram for describing a relationship between a coding unit710 and transformation units 720, according to an embodiment of thepresent invention.

The video encoding apparatus 100 or the video decoding apparatus 200encodes or decodes an image according to coding units having sizessmaller than or equal to a maximum coding unit for each maximum codingunit. Sizes of transformation units for transformation during encodingmay be selected based on data units that are not larger than acorresponding coding unit.

For example, in the video encoding apparatus 100 or the video decodingapparatus 200, if a size of the coding unit 710 is 64×64, transformationmay be performed by using the transformation units 720 having a size of32×32.

Also, data of the coding unit 710 having the size of 64×64 may beencoded by performing the transformation on each of the transformationunits having the size of 32×32, 16×16, 8×8, and 4×4, which are smallerthan 64×64, and then a transformation unit having the least coding errormay be selected.

FIG. 13 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an embodiment of thepresent invention.

The output unit 130 of the video encoding apparatus 100 may encode andtransmit information 800 about a partition type, information 810 about aprediction mode, and information 820 about a size of a transformationunit for each coding unit corresponding to a coded depth, as informationabout an encoding mode.

The information 800 indicates information about a shape of a partitionobtained by splitting a prediction unit of a current coding unit,wherein the partition is a data unit for prediction encoding the currentcoding unit. For example, a current coding unit CU_0 having a size of2N×2N may be split into any one of a partition 802 having a size of2N×2N, a partition 804 having a size of 2N×N, a partition 806 having asize of N×2N, and a partition 808 having a size of N×N. Here, theinformation 800 about a partition type is set to indicate one of thepartition 804 having a size of 2N×N, the partition 806 having a size ofN×2N, and the partition 808 having a size of N×N.

The information 810 indicates a prediction mode of each partition. Forexample, the information 810 may indicate a mode of prediction encodingperformed on a partition indicated by the information 800, i.e., anintra mode 812, an inter mode 814, or a skip mode 816.

The information 820 indicates a transformation unit to be based on whentransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second inter transformation unit 828.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information 800, 810, and820 for decoding, according to each deeper coding unit.

FIG. 14 is a diagram of deeper coding units according to depths,according to an embodiment of the present invention.

Split information may be used to indicate a change of a depth. The spiltinformation indicates whether a coding unit of a current depth is splitinto coding units of a lower depth.

A prediction unit 910 for prediction encoding a coding unit 900 having adepth of 0 and a size of 2N_0×2N_0 may include partitions of a partitiontype 912 having a size of 2N_0×2N_0, a partition type 914 having a sizeof 2N_0×N_0, a partition type 916 having a size of N_0×2N_0, and apartition type 918 having a size of N_0×N_0. FIG. 14 only illustratesthe partition types 912 through 918 which are obtained by symmetricallysplitting the prediction unit 910, but a partition type is not limitedthereto, and the partitions of the prediction unit 910 may includeasymmetrical partitions, partitions having a predetermined shape, andpartitions having a geometrical shape.

Prediction encoding is repeatedly performed on one partition having asize of 2N_0×2N_0, two partitions having a size of 2N_0×N_0, twopartitions having a size of N_0×2N_0, and four partitions having a sizeof N_0×N_0, according to each partition type. The prediction encoding inan intra mode and an inter mode may be performed on the partitionshaving the sizes of 2N_0×2N_0, N_0×2N_0, 2N_0×N_0, and N_0×N_0. Theprediction encoding in a skip mode is performed only on the partitionhaving the size of 2N_0×2N_0.

If an encoding error is smallest in one of the partition types 912through 916, the prediction unit 910 may not be split into a lowerdepth.

If the encoding error is the smallest in the partition type 918, a depthis changed from 0 to 1 to split the partition type 918 in operation 920,and encoding is repeatedly performed on coding units 930 having a depthof 2 and a size of N_0×N_0 to search for a minimum encoding error.

A prediction unit 940 for prediction encoding the coding unit 930 havinga depth of 1 and a size of 2N_1×2N_1 (=N_0×N_0) may include partitionsof a partition type 942 having a size of 2N_1×2N_1, a partition type 944having a size of 2N_1×N_1, a partition type 946 having a size ofN_1×2N_1, and a partition type 948 having a size of N_1×N_1.

If an encoding error is the smallest in the partition type 948, a depthis changed from 1 to 2 to split the partition type 948 in operation 950,and encoding is repeatedly performed on coding units 960, which have adepth of 2 and a size of N_2×N_2 to search for a minimum encoding error.

When a maximum depth is d, split operation according to each depth maybe performed up to when a depth becomes d−1, and split information maybe encoded as up to when a depth is one of 0 to d−2. In other words,when encoding is performed up to when the depth is d−1 after a codingunit corresponding to a depth of d−2 is split in operation 970, aprediction unit 990 for prediction encoding a coding unit 980 having adepth of d−1 and a size of 2N_(d−1)×2N_(d−1) may include partitions of apartition type 992 having a size of 2N_(d−1)×2N_(d−1), a partition type994 having a size of 2N_(d−1)×N_(d−1), a partition type 996 having asize of N_(d−1)×2N_(d−1), and a partition type 998 having a size ofN_(d−1)×N_(d−1).

Prediction encoding may be repeatedly performed on one partition havinga size of 2N_(d−1)×2N_(d−1), two partitions having a size of2N_(d−1)×N_(d−1), two partitions having a size of N_(d−1)×2N_(d−1), fourpartitions having a size of N_(d−1)×N_(d−1) from among the partitiontypes 992 through 998 to search for a partition type having a minimumencoding error.

Even when the partition type 998 has the minimum encoding error, since amaximum depth is d, a coding unit CU_(d−1) having a depth of d−1 is nolonger split to a lower depth, and a coded depth for the coding unitsconstituting a current maximum coding unit 900 is determined to be d−1and a partition type of the current maximum coding unit 900 may bedetermined to be N_(d−1)×N_(d−1). Also, since the maximum depth is d anda minimum coding unit 980 having a lowermost depth of d−1 is no longersplit to a lower depth, split information for the minimum coding unit980 is not set.

A data unit 999 may be a ‘minimum unit’ for the current maximum codingunit. A minimum unit according to an embodiment of the present inventionmay be a square data unit obtained by splitting a minimum coding unit980 by 4. By performing the encoding repeatedly, the video encodingapparatus 100 may select a depth having the least encoding error bycomparing encoding errors according to depths of the coding unit 900 todetermine a coded depth, and set a corresponding partition type and aprediction mode as an encoding mode of the coded depth.

As such, the minimum encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a coded depth. The coded depth, the partitiontype of the prediction unit, and the prediction mode may be encoded andtransmitted as information about an encoding mode. Also, since a codingunit is split from a depth of 0 to a coded depth, only split informationof the coded depth is set to 0, and split information of depthsexcluding the coded depth is set to 1.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information about thecoded depth and the prediction unit of the coding unit 900 to decode thepartition 912. The video decoding apparatus 200 may determine a depth,in which split information is 0, as a coded depth by using splitinformation according to depths, and use information about an encodingmode of the corresponding depth for decoding.

FIGS. 15 through 17 are diagrams for describing a relationship betweencoding units 1010, prediction units 1060, and transformation units 1070,according to an embodiment of the present invention.

The coding units 1010 are coding units having a tree structure,corresponding to coded depths determined by the video encoding apparatus100, in a maximum coding unit. The prediction units 1060 are partitionsof prediction units of each of the coding units 1010, and thetransformation units 1070 are transformation units of each of the codingunits 1010.

When a depth of a maximum coding unit is 0 in the coding units 1010,depths of coding units 1012 and 1054 are 1, depths of coding units 1014,1016, 1018, 1028, 1050, and 1052 are 2, depths of coding units 1020,1022, 1024, 1026, 1030, 1032, and 1048 are 3, and depths of coding units1040, 1042, 1044, and 1046 are 4.

In the prediction units 1060, some encoding units 1014, 1016, 1022,1032, 1048, 1050, 1052, and 1054 are obtained by splitting the codingunits in the encoding units 1010. In other words, partition types in thecoding units 1014, 1022, 1050, and 1054 have a size of 2N×N, partitiontypes in the coding units 1016, 1048, and 1052 have a size of N×2N, anda partition type of the coding unit 1032 has a size of N×N. Predictionunits and partitions of the coding units 1010 are smaller than or equalto each coding unit.

Transformation or inverse transformation is performed on image data ofthe coding unit 1052 in the transformation units 1070 in a data unitthat is smaller than the coding unit 1052. Also, the coding units 1014,1016, 1022, 1032, 1048, 1050, and 1052 in the transformation units 1070are different from those in the prediction units 1060 in terms of sizesand shapes. In other words, the video encoding and decoding apparatuses100 and 200 may perform intra prediction, motion estimation, motioncompensation, transformation, and inverse transformation individually ona data unit in the same coding unit.

Accordingly, encoding is recursively performed on each of coding unitshaving a hierarchical structure in each region of a maximum coding unitto determine an optimum coding unit, and thus coding units having arecursive tree structure may be obtained. Encoding information mayinclude split information about a coding unit, information about apartition type, information about a prediction mode, and informationabout a size of a transformation unit. Table 1 shows the encodinginformation that may be set by the video encoding and decodingapparatuses 100 and 200.

TABLE 1 Split Split Information 0 Information (Encoding on Coding Unithaving Size of 2N × 2N and Current Depth of d) 1 Prediction PartitionType Size of Transformation Unit Repeatedly Mode Encode IntraSymmetrical Asymmetrical Split Split Coding Inter Partition PartitionInformation 0 Information 1 Units Skip Type Type of of having (OnlyTransformation Transformation Lower 2N × 2N) Unit Unit Depth of 2N × 2N2N × nU 2N × 2N N × N d + 1 2N × N  2N × nD (Symmetrical  N × 2N nL × 2NType) N × N nR × 2N N/2 × N/2 (Asymmetrical Type)

The output unit 130 of the video encoding apparatus 100 may output theencoding information about the coding units having a tree structure, andthe image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract the encoding information about thecoding units having a tree structure from a received bitstream.

Split information indicates whether a current coding unit is split intocoding units of a lower depth. If split information of a current depth dis 0, a depth, in which a current coding unit is no longer split into alower depth, is a coded depth, and thus information about a partitiontype, prediction mode, and a size of a transformation unit may bedefined for the coded depth. If the current coding unit is further splitaccording to the split information, encoding is independently performedon four split coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitiontypes, and the skip mode is defined only in a partition type having asize of 2N×2N.

The information about the partition type may indicate symmetricalpartition types having sizes of 2N×2N, 2N×N, N×2N, and N×N, which areobtained by symmetrically splitting a height or a width of a predictionunit, and asymmetrical partition types having sizes of 2N×nU, 2N×nD,nL×2N, and nR×2N, which are obtained by asymmetrically splitting theheight or width of the prediction unit. The asymmetrical partition typeshaving the sizes of 2N×nU and 2N×nD may be respectively obtained bysplitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition types having the sizes of nL×2N and nR×2N may berespectively obtained by splitting the width of the prediction unit in1:3 and 3:1

The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splitinformation of the transformation unit is 0, the size of thetransformation unit may be 2N×2N, which is the size of the currentcoding unit. If split information of the transformation unit is 1, thetransformation units may be obtained by splitting the current codingunit. Also, if a partition type of the current coding unit having thesize of 2N×2N is a symmetrical partition type, a size of atransformation unit may be N×N, and if the partition type of the currentcoding unit is an asymmetrical partition type, the size of thetransformation unit may be N/2×N/2.

The encoding information about coding units having a tree structure mayinclude at least one of a coding unit corresponding to a coded depth, aprediction unit, and a minimum unit. The coding unit corresponding tothe coded depth may include at least one of a prediction unit and aminimum unit containing the same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the coded depth by comparingencoding information of the adjacent data units. Also, a correspondingcoding unit corresponding to a coded depth is determined by usingencoding information of a data unit, and thus a distribution of codeddepths in a maximum coding unit may be determined.

Accordingly, if a current coding unit is predicted based on encodinginformation of adjacent data units, encoding information of data unitsin deeper coding units adjacent to the current coding unit may bedirectly referred to and used.

Alternatively, if a current coding unit is predicted based on encodinginformation of adjacent data units, data units adjacent to the currentcoding unit are searched using encoded information of the data units,and the searched adjacent coding units may be referred for predictingthe current coding unit.

FIG. 18 is a diagram for describing a relationship between a codingunit, a prediction unit, and a transformation unit, according toencoding mode information of Table 1.

A maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312,1314, 1316, and 1318 of coded depths. Here, since the coding unit 1318is a coding unit of a coded depth, split information may be set to 0.Information about a partition type of the coding unit 1318 having a sizeof 2N×2N may be set to be one of a partition type 1322 having a size of2N×2N, a partition type 1324 having a size of 2N×N, a partition type1326 having a size of N×2N, a partition type 1328 having a size of N×N,a partition type 1332 having a size of 2N×nU, a partition type 1334having a size of 2N×nD, a partition type 1336 having a size of nL×2N,and a partition type 1338 having a size of nR×2N.

Split information (TU size flag) of a transformation unit is a type of atransformation index. The size of the transformation unit correspondingto the transformation index may be changed according to a predictionunit type or partition type of the coding unit.

For example, when the partition type is set to be symmetrical, i.e. thepartition type 1322, 1324, 1326, or 1328, a transformation unit 1342having a size of 2N×2N is set if a TU size flag of a transformation unitis 0, and a transformation unit 1344 having a size of N×N is set if a TUsize flag is 1.

When the partition type is set to be asymmetrical, i.e., the partitiontype 1332, 1334, 1336, or 1338, a transformation unit 1352 having a sizeof 2N×2N is set if a TU size flag is 0, and a transformation unit 1354having a size of N/2×N/2 is set if a TU size flag is 1.

Referring to FIG. 18, the TU size flag is a flag having a value or 0 or1, but the TU size flag is not limited to 1 bit, and a transformationunit may be hierarchically split having a tree structure while the TUsize flag increases from 0. Split information (TU size flag) of atransformation unit may be an example of a transformation index.

In this case, the size of a transformation unit that has been actuallyused may be expressed by using a TU size flag of a transformation unit,according to an embodiment according to the present invention, togetherwith a maximum size and minimum size of the transformation unit. Thevideo encoding apparatus 100 is capable of encoding maximumtransformation unit size information, minimum transformation unit sizeinformation, and a maximum TU size flag. The result of encoding themaximum transformation unit size information, the minimum transformationunit size information, and the maximum TU size flag may be inserted intoan SPS. The video decoding apparatus 200 may decode video by using themaximum transformation unit size information, the minimum transformationunit size information, and the maximum TU size flag.

For example, (a) if the size of a current coding unit is 64×64 and amaximum transformation unit size is 32×32, (a-1) then the size of atransformation unit may be 32×32 when a TU size flag is 0, (a-2) may be16×16 when the TU size flag is 1, and (a-3) may be 8×8 when the TU sizeflag is 2.

As another example, (b) if the size of the current coding unit is 32×32and a minimum transformation unit size is 32×32, (b-1) then the size ofthe transformation unit may be 32×32 when the TU size flag is 0. Here,the TU size flag cannot be set to a value other than 0, since the sizeof the transformation unit cannot be less than 32×32.

As another example, (c) if the size of the current coding unit is 64×64and a maximum TU size flag is 1, then the TU size flag may be 0 or 1.Here, the TU size flag cannot be set to a value other than 0 or 1.

Thus, if it is defined that the maximum TU size flag is‘MaxTransformSizeIndex’, a minimum transformation unit size is‘MinTransformSize’, and a transformation unit size is ‘RootTuSize’ whenthe TU size flag is 0, then a current minimum transformation unit size‘CurrMinTuSize’ that can be determined in a current coding unit, may bedefined by Equation (1):

CurrMinTuSize=max(MinTransformSize,RootTuSize/(2∧MaxTransformSizeIndex))  (1)

Compared to the current minimum transformation unit size ‘CurrMinTuSize’that can be determined in the current coding unit, a transformation unitsize ‘RootTuSize’ when the TU size flag is 0 may denote a maximumtransformation unit size that can be selected in the system. In Equation(1), ‘RootTuSize/(2∧MaxTransformSizeIndex)’ denotes a transformationunit size when the transformation unit size ‘RootTuSize’, when the TUsize flag is 0, is split a number of times corresponding to the maximumTU size flag, and ‘MinTransformSize’ denotes a minimum transformationsize. Thus, a smaller value from among‘RootTuSize/(2∧MaxTransformSizeIndex)’ and ‘MinTransformSize’ may be thecurrent minimum transformation unit size ‘CurrMinTuSize’ that can bedetermined in the current coding unit.

According to an embodiment according to the present invention, themaximum transformation unit size RootTuSize may vary according to thetype of a prediction mode.

For example, if a current prediction mode is an inter mode, then‘RootTuSize’ may be determined by using Equation (2) below. In Equation(2), ‘MaxTransformSize’ denotes a maximum transformation unit size, and‘PUSize’ denotes a current prediction unit size.

RootTuSize=min(MaxTransformSize,PUSize)  (2)

That is, if the current prediction mode is the inter mode, thetransformation unit size ‘RootTuSize’, when the TU size flag is 0, maybe a smaller value from among the maximum transformation unit size andthe current prediction unit size.

If a prediction mode of a current partition unit is an intra mode,‘RootTuSize’ may be determined by using Equation (3) below. In Equation(3), ‘PartitionSize’ denotes the size of the current partition unit.

RootTuSize=min(MaxTransformSize,PartitionSize)  (3)

That is, if the current prediction mode is the intra mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0 may bea smaller value from among the maximum transformation unit size and thesize of the current partition unit.

However, the current maximum transformation unit size ‘RootTuSize’ thatvaries according to the type of a prediction mode in a partition unit isjust an example and the present invention is not limited thereto.

According to the video encoding method based on coding units having atree structure as described with reference to FIGS. 6 through 18, imagedata of a spatial region is encoded for each coding unit of a treestructure. According to the video decoding method based on coding unitshaving a tree structure, decoding is performed for each maximum codingunit to restore image data of a spatial region. Thus, a picture and avideo that is a picture sequence may be restored. The restored video maybe reproduced by a reproducing apparatus, stored in a storage medium, ortransmitted through a network.

The embodiments according to the present invention may be written ascomputer programs and may be implemented in general-use digitalcomputers that execute the programs using a computer-readable recordingmedium. Examples of the computer-readable recording medium includemagnetic storage media (e.g., ROM, floppy discs, hard discs, etc.) andoptical recording media (e.g., CD-ROMs, or DVDs).

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeaccording to the present invention as defined by the following claims.

As programs for realizing the inter prediction method, the motioncompensation method, the video encoding method, and the video decodingmethod described with reference to FIGS. 1 through 18 are stored in thecomputer-readable recording media, an independent computer system mayeasily realize operations according to the programs stored in thecomputer-readable recording media.

For convenience of description, the inter prediction method and thevideo encoding method described with reference to FIGS. 1 through 18,will be collectively referred to as a ‘video encoding method accordingto the present invention’. In addition, the motion compensation methodand the video decoding method described with reference to FIGS. 1through 18, will be referred to as a ‘video decoding method according tothe present invention’.

Also, a video encoding apparatus including the inter predictionapparatus 10, the video encoding apparatus 40, the video encodingapparatus 100, or the image encoder 400, which has been described withreference to FIGS. 1 through 18, will be referred to as a ‘videoencoding apparatus according to the present invention’. In addition, avideo decoding apparatus including the motion compensation apparatus 20,the video decoding apparatus 50, the video decoding apparatus 200, orthe image decoder 500, which has been descried with reference to FIGS. 1through 18, will be referred to as a ‘video decoding apparatus accordingto the present invention’.

A computer-readable recording medium storing a program, e.g., a disc26000, according to an embodiment of the present invention will now bedescribed in detail.

FIG. 19 is a diagram of a physical structure of the disc 26000 in whicha program is stored, according to an embodiment of the presentinvention. The disc 26000, which is a storage medium, may be a harddrive, a compact disc-read only memory (CD-ROM) disc, a Blu-ray disc, ora digital versatile disc (DVD). The disc 26000 includes a plurality ofconcentric tracks Tr that are each divided into a specific number ofsectors Se in a circumferential direction of the disc 26000. In aspecific region of the disc 26000, a program that executes the interprediction method, the motion compensation method, the video encodingmethod, and the video decoding method described above may be assignedand stored.

A computer system embodied using a storage medium that stores a programfor executing the video encoding method and the video decoding method asdescribed above will now be described with reference to FIG. 20.

FIG. 20 is a diagram of a disc drive 26800 for recording and reading aprogram by using the disc 26000. A computer system 27000 may store aprogram that executes at least one of a video encoding method and avideo decoding method according to an embodiment of the presentinvention, in the disc 26000 via the disc drive 26800. To run theprogram stored in the disc 26000 in the computer system 27000, theprogram may be read from the disc 26000 and be transmitted to thecomputer system 27000 by using the disc drive 26800.

The program that executes at least one of a video encoding method and avideo decoding method according to an embodiment of the presentinvention may be stored not only in the disc 26000 illustrated in FIG.19 or 20 but also in a memory card, a ROM cassette, or a solid statedrive (SSD).

A system to which the video encoding method and a video decoding methoddescribed above are applied will be described below.

FIG. 21 is a diagram of an overall structure of a content supply system11000 for providing a content distribution service. A service area of acommunication system is divided into predetermined-sized cells, andwireless base stations 11700, 11800, 11900, and 12000 are installed inthese cells, respectively.

The content supply system 11000 includes a plurality of independentdevices. For example, the plurality of independent devices, such as acomputer 12100, a personal digital assistant (PDA) 12200, a video camera12300, and a mobile phone 12500, are connected to the Internet 11100 viaan internet service provider 11200, a communication network 11400, andthe wireless base stations 11700, 11800, 11900, and 12000.

However, the content supply system 11000 is not limited to asillustrated in FIG. 21, and devices may be selectively connectedthereto. The plurality of independent devices may be directly connectedto the communication network 11400, not via the wireless base stations11700, 11800, 11900, and 12000.

The video camera 12300 is an imaging device, e.g., a digital videocamera, which is capable of capturing video images. The mobile phone12500 may employ at least one communication method from among variousprotocols, e.g., Personal Digital Communications (PDC), Code DivisionMultiple Access (CDMA), Wideband-Code Division Multiple Access (W-CDMA),Global System for Mobile Communications (GSM), and Personal HandyphoneSystem (PHS).

The video camera 12300 may be connected to a streaming server 11300 viathe wireless base station 11900 and the communication network 11400. Thestreaming server 11300 allows content received from a user via the videocamera 12300 to be streamed via a real-time broadcast. The contentreceived from the video camera 12300 may be encoded using the videocamera 12300 or the streaming server 11300. Video data captured by thevideo camera 12300 may be transmitted to the streaming server 11300 viathe computer 12100.

Video data captured by a camera 12600 may also be transmitted to thestreaming server 11300 via the computer 12100. The camera 12600 is animaging device capable of capturing both still images and video images,similar to a digital camera. The video data captured by the camera 12600may be encoded using the camera 12600 or the computer 12100. Softwarethat performs encoding and decoding video may be stored in acomputer-readable recording medium, e.g., a CD-ROM disc, a floppy disc,a hard disc drive, an SSD, or a memory card, which may be accessible bythe computer 12100.

If video data is captured by a camera built in the mobile phone 12500,the video data may be received from the mobile phone 12500.

The video data may also be encoded by a large scale integrated circuit(LSI) system installed in the video camera 12300, the mobile phone12500, or the camera 12600.

The content supply system 11000 may encode content data recorded by auser using the video camera 12300, the camera 12600, the mobile phone12500, or another imaging device, e.g., content recorded during aconcert, and transmit the encoded content data to the streaming server11300. The streaming server 11300 may transmit the encoded content datain a type of a streaming content to other clients that request thecontent data.

The clients are devices capable of decoding the encoded content data,e.g., the computer 12100, the PDA 12200, the video camera 12300, or themobile phone 12500. Thus, the content supply system 11000 allows theclients to receive and reproduce the encoded content data. Also, thecontent supply system 11000 allows the clients to receive the encodedcontent data and decode and reproduce the encoded content data in realtime, thereby enabling personal broadcasting.

Encoding and decoding operations of the plurality of independent devicesincluded in the content supply system 11000 may be similar to those of avideo encoding apparatus and a video decoding apparatus according to anembodiment of the present invention.

The mobile phone 12500 included in the content supply system 11000according to an embodiment of the present invention will now bedescribed in greater detail with referring to FIGS. 22 and 23.

FIG. 22 illustrates an external structure of the mobile phone 12500 towhich a video encoding method and a video decoding method are applied,according to an embodiment of the present invention. The mobile phone12500 may be a smart phone, the functions of which are not limited and alarge number of the functions of which may be changed or expanded.

The mobile phone 12500 includes an internal antenna 12510 via which aradio-frequency (RF) signal may be exchanged with the wireless basestation 12000 of FIG. 21, and includes a display screen 12520 fordisplaying images captured by a camera 12530 or images that are receivedvia the antenna 12510 and decoded, e.g., a liquid crystal display (LCD)or an organic light-emitting diode (OLED) screen. The mobile phone 12500includes an operation panel 12540 including a control button and a touchpanel. If the display screen 12520 is a touch screen, the operationpanel 12540 further includes a touch sensing panel of the display screen12520. The mobile phone 12500 includes a speaker 12580 for outputtingvoice and sound or another type of sound output unit, and a microphone12550 for inputting voice and sound or another type sound input unit.The mobile phone 12500 further includes the camera 12530, such as acharge-coupled device (CCD) camera, to capture video and still images.The mobile phone 12500 may further include a storage medium 12570 forstoring encoded/decoded data, e.g., video or still images captured bythe camera 12530, received via email, or obtained according to variousways; and a slot 12560 via which the storage medium 12570 is loaded intothe mobile phone 12500. The storage medium 12570 may be a flash memory,e.g., a secure digital (SD) card or an electrically erasable andprogrammable read only memory (EEPROM) included in a plastic case.

FIG. 23 illustrates an internal structure of the mobile phone 12500,according to an embodiment of the present invention. To systemicallycontrol parts of the mobile phone 12500 including the display screen12520 and the operation panel 12540, a power supply circuit 12700, anoperation input controller 12640, an image encoding unit 12720, a camerainterface 12630, an LCD controller 12620, an image decoding unit 12690,a multiplexer/demultiplexer 12680, a recording/reading unit 12670, amodulation/demodulation unit 12660, and a sound processor 12650 areconnected to a central controller 12710 via a synchronization bus 12730.

If a user operates a power button and sets from a ‘power off’ state to apower on’ state, the power supply circuit 12700 supplies power to allthe parts of the mobile phone 12500 from a battery pack, thereby settingthe mobile phone 12500 in an operation mode.

The central controller 12710 includes a central processing unit (CPU), aROM, and a RAM.

While the mobile phone 12500 transmits communication data to theoutside, a digital signal is generated by the mobile phone 12500 undercontrol of the central controller 12710. For example, the soundprocessor 12650 may generate a digital sound signal, the image encodingunit 12720 may generate a digital image signal, and text data of amessage may be generated via the operation panel 12540 and the operationinput controller 12640. When a digital signal is transmitted to themodulation/demodulation unit 12660 under control of the centralcontroller 12710, the modulation/demodulation unit 12660 modulates afrequency band of the digital signal, and a communication circuit 12610performs digital-to-analog conversion (DAC) and frequency conversion onthe frequency band-modulated digital sound signal. A transmission signaloutput from the communication circuit 12610 may be transmitted to avoice communication base station or the wireless base station 12000 viathe antenna 12510.

For example, when the mobile phone 12500 is in a conversation mode, asound signal obtained via the microphone 12550 is transformed into adigital sound signal by the sound processor 12650, under control of thecentral controller 12710. The digital sound signal may be transformedinto a transformation signal via the modulation/demodulation unit 12660and the communication circuit 12610, and may be transmitted via theantenna 12510.

When a text message, e.g., email, is transmitted in a data communicationmode, text data of the text message is input via the operation panel12540 and is transmitted to the central controller 12710 via theoperation input controller 12640. Under control of the centralcontroller 12710, the text data is transformed into a transmissionsignal via the modulation/demodulation unit 12660 and the communicationcircuit 12610 and is transmitted to the wireless base station 12000 viathe antenna 12510.

To transmit image data in the data communication mode, image datacaptured by the camera 12530 is provided to the image encoding unit12720 via the camera interface 12630. The captured image data may bedirectly displayed on the display screen 12520 via the camera interface12630 and the LCD controller 12620.

A structure of the image encoding unit 12720 may correspond to that ofthe video encoding apparatus 100 described above. The image encodingunit 12720 may transform the image data received from the camera 12530into compressed and encoded image data according to a video encodingmethod employed by the video encoding apparatus 100 or the image encoder400 described above, and then output the encoded image data to themultiplexer/demultiplexer 12680. During a recording operation of thecamera 12530, a sound signal obtained by the microphone 12550 of themobile phone 12500 may be transformed into digital sound data via thesound processor 12650, and the digital sound data may be transmitted tothe multiplexer/demultiplexer 12680.

The multiplexer/demultiplexer 12680 multiplexes the encoded image datareceived from the image encoding unit 12720, together with the sounddata received from the sound processor 12650. A result of multiplexingthe data may be transformed into a transmission signal via themodulation/demodulation unit 12660 and the communication circuit 12610,and may then be transmitted via the antenna 12510.

While the mobile phone 12500 receives communication data from theoutside, frequency recovery and ADC are performed on a signal receivedvia the antenna 12510 to transform the signal into a digital signal. Themodulation/demodulation unit 12660 modulates a frequency band of thedigital signal. The frequency-band modulated digital signal istransmitted to the video decoding unit 12690, the sound processor 12650,or the LCD controller 12620, according to the type of the digitalsignal.

In the conversation mode, the mobile phone 12500 amplifies a signalreceived via the antenna 12510, and obtains a digital sound signal byperforming frequency conversion and ADC on the amplified signal. Areceived digital sound signal is transformed into an analog sound signalvia the modulation/demodulation unit 12660 and the sound processor12650, and the analog sound signal is output via the speaker 12580,under control of the central controller 12710.

When in the data communication mode, data of a video file accessed at anInternet website is received, a signal received from the wireless basestation 12000 via the antenna 12510 is output as multiplexed data viathe modulation/demodulation unit 12660, and the multiplexed data istransmitted to the multiplexer/demultiplexer 12680.

To decode the multiplexed data received via the antenna 12510, themultiplexer/demultiplexer 12680 demultiplexes the multiplexed data intoan encoded video data stream and an encoded audio data stream. Via thesynchronization bus 12730, the encoded video data stream and the encodedaudio data stream are provided to the video decoding unit 12690 and thesound processor 12650, respectively.

A structure of the image decoding unit 12690 may correspond to that ofthe video decoding apparatus 200 described above. The image decodingunit 12690 may decode the encoded video data to obtain restored videodata and provide the restored video data to the display screen 12520 viathe LCD controller 12620, according to a video decoding method employedby the video decoding apparatus 200 or the image decoder 500 describedabove.

Thus, the data of the video file accessed at the Internet website may bedisplayed on the display screen 12520. At the same time, the soundprocessor 12650 may transform audio data into an analog sound signal,and provide the analog sound signal to the speaker 12580. Thus, audiodata contained in the video file accessed at the Internet website mayalso be reproduced via the speaker 12580.

The mobile phone 12500 or another type of communication terminal may bea transceiving terminal including both a video encoding apparatus and avideo decoding apparatus according to an embodiment of the presentinvention, may be a transceiving terminal including only the videoencoding apparatus, or may be a transceiving terminal including only thevideo decoding apparatus.

A communication system according to the present invention is not limitedto the communication system described above with reference to FIG. 21.For example, FIG. 24 illustrates a digital broadcasting system employinga communication system, according to an embodiment of the presentinvention. The digital broadcasting system of FIG. 24 may receive adigital broadcast transmitted via a satellite or a terrestrial networkby using a video encoding apparatus and a video decoding apparatusaccording to an embodiment of the present invention.

Specifically, a broadcasting station 12890 transmits a video data streamto a communication satellite or a broadcasting satellite 12900 by usingradio waves. The broadcasting satellite 12900 transmits a broadcastsignal, and the broadcast signal is transmitted to a satellite broadcastreceiver via a household antenna 12860. In every house, an encoded videostream may be decoded and reproduced by a TV receiver 12810, a set-topbox 12870, or another device.

When a video decoding apparatus according to an embodiment of thepresent invention is implemented in a reproducing apparatus 12830, thereproducing apparatus 12830 may parse and decode an encoded video streamrecorded on a storage medium 12820, such as a disc or a memory card torestore digital signals. Thus, the restored video signal may bereproduced, for example, on a monitor 12840.

In the set-top box 12870 connected to the antenna 12860 for asatellite/terrestrial broadcast or a cable antenna 12850 for receiving acable television (TV) broadcast, a video decoding apparatus according toan embodiment of the present invention may be installed. Data outputfrom the set-top box 12870 may also be reproduced on a TV monitor 12880.

As another example, a video decoding apparatus according to anembodiment of the present invention may be installed in the TV receiver12810 instead of the set-top box 12870.

An automobile 12920 that has an appropriate antenna 12910 may receive asignal transmitted from the satellite 12900 or the wireless base station11700 of FIG. 21. A decoded video may be reproduced on a display screenof an automobile navigation system 12930 installed in the automobile12920.

A video signal may be encoded by a video encoding apparatus according toan embodiment of the present invention and may then be stored in astorage medium. Specifically, an image signal may be stored in a DVDdisc 12960 by a

DVD recorder or may be stored in a hard disc by a hard disc recorder12950. As another example, the video signal may be stored in an SD card12970. If the hard disc recorder 12950 includes a video decodingapparatus according to an embodiment of the present invention, a videosignal recorded on the DVD disc 12960, the SD card 12970, or anotherstorage medium may be reproduced on the TV monitor 12880.

The automobile navigation system 12930 may not include the camera 12530,the camera interface 12630, and the image encoding unit 12720 of FIG.23. For example, the computer 12100 and the TV receiver 12810 may not beincluded in the camera 12530, the camera interface 12630, and the imageencoding unit 12720 of FIG. 23.

FIG. 25 is a diagram illustrating a network structure of a cloudcomputing system using a video encoding apparatus and a video decodingapparatus, according to an embodiment of the present invention.

The cloud computing system may include a cloud computing server 14000, auser database (DB) 14100, a plurality of computing resources 14200, anda user terminal.

The cloud computing system provides an on-demand outsourcing service ofthe plurality of computing resources 14200 via a data communicationnetwork, e.g., the Internet, in response to a request from the userterminal. Under a cloud computing environment, a service providerprovides users with desired services by combining computing resources atdata centers located at physically different locations by usingvirtualization technology. A service user does not have to installcomputing resources, e.g., an application, a storage, an operatingsystem (OS), and security, into his/her own terminal in order to usethem, but may select and use desired services from among services in avirtual space generated through the virtualization technology, at adesired point in time.

A user terminal of a specified service user is connected to the cloudcomputing server 14000 via a data communication network including theInternet and a mobile telecommunication network. User terminals may beprovided cloud computing services, and particularly video reproductionservices, from the cloud computing server 14000. The user terminals maybe various types of electronic devices capable of being connected to theInternet, e.g., a desktop PC 14300, a smart TV 14400, a smart phone14500, a notebook computer 14600, a portable multimedia player (PMP)14700, a tablet PC 14800, and the like.

The cloud computing server 14000 may combine the plurality of computingresources 14200 distributed in a cloud network and provide userterminals with a result of combining. The plurality of computingresources 14200 may include various data services, and may include datauploaded from user terminals. As described above, the cloud computingserver 14000 may provide user terminals with desired services bycombining video database distributed in different regions according tothe virtualization technology.

User information about users who have subscribed for a cloud computingservice is stored in the user DB 14100. The user information may includelogging information, addresses, names, and personal credit informationof the users. The user information may further include indexes ofvideos. Here, the indexes may include a list of videos that have alreadybeen reproduced, a list of videos that are being reproduced, a pausingpoint of a video that was being reproduced, and the like.

Information about a video stored in the user DB 14100 may be sharedbetween user devices. For example, when a video service is provided tothe notebook computer 14600 in response to a request from the notebookcomputer 14600, a reproduction history of the video service is stored inthe user DB 14100. When a request to reproduce this video service isreceived from the smart phone 14500, the cloud computing server 14000searches for and reproduces this video service, based on the user DB14100. When the smart phone 14500 receives a video data stream from thecloud computing server 14000, a process of reproducing video by decodingthe video data stream is similar to an operation of the mobile phone12500 described above with reference to FIGS. 22 and 23.

The cloud computing server 14000 may refer to a reproduction history ofa desired video service, stored in the user DB 14100. For example, thecloud computing server 14000 receives a request to reproduce a videostored in the user DB 14100, from a user terminal. If this video wasbeing reproduced, then a method of streaming this video, performed bythe cloud computing server 14000, may vary according to the request fromthe user terminal, i.e., according to whether the video will bereproduced, starting from a start thereof or a pausing point thereof.For example, if the user terminal requests to reproduce the video,starting from the start thereof, the cloud computing server 14000transmits streaming data of the video starting from a first framethereof to the user terminal. If the user terminal requests to reproducethe video, starting from the pausing point thereof, the cloud computingserver 14000 transmits streaming data of the video starting from a framecorresponding to the pausing point, to the user terminal.

In this case, the user terminal may include a video decoding apparatusas described above with reference to FIGS. 1 to 18. As another example,the user terminal may include a video encoding apparatus as describedabove with reference to FIGS. 1 to 18. Alternatively, the user terminalmay include both the video decoding apparatus and the video encodingapparatus as described above with reference to FIGS. 1 to 18.

Various applications of a video encoding method, a video decodingmethod, a video encoding apparatus, and a video decoding apparatusaccording to embodiments of the present invention described above withreference to FIGS. 1 to 18 have been described above with reference toFIGS. 19 to 25. However, methods of storing the video encoding methodand the video decoding method in a storage medium or methods ofimplementing the video encoding apparatus and the video decodingapparatus in a device, according to various embodiments of the presentinvention, are not limited to the embodiments described above withreference to FIGS. 19 to 25.

What is claimed is:
 1. A video decoding apparatus comprising: a receiver to receive a bitstream; and a motion compensator to obtain, from the bitstream, LSB (Least Significant Bits) information regarding picture order count (POC) information of a current long-term reference image of a current image, to determine MSB (Most Significant Bits) information regarding the POC information of the current long-term reference image of the current image based on MSB information regarding POC information of a previous long-term reference image of the current image and a difference between the MSB information regarding the POC information of the current long-term reference image and the MSB information regarding the POC information of the previous long-term reference image of the current image, to determine the POC information of the current long-term reference image of the current image by using the LSB information and the MSB information regarding the POC information of the current long-term reference image of the current image, and to reconstruct the current image by using the current long-term reference image of the current image corresponding to the POC information of the current long-term reference image of the current image, wherein the MSB information regarding POC (Picture Order Count) information of the current long-term reference image of the current image is information regarding a quotient generated by dividing a value related to the POC information of the current long-term reference image of the current image by a maximum size of the LSB information, and the LSB information is information regarding a remainder value generated by dividing the POC information of the current long-term reference image of the current image by the maximum size of the LSB information.
 2. A video encoding apparatus comprising: an inter predictor to perform an inter prediction on a current image by using a current long-term reference image of the current image; and an outputter to obtain POC information of the current long-term reference image of the current image corresponding to the current long-term reference image of the current image, generate LSB information regarding the POC information of the current long-term reference image of the current image, and generate a bitstream including LSB information regarding POC information of the current long-term reference image of the current image, wherein the LSB information is information regarding a remainder value generated by dividing the POC information of the current long-term reference image of the current image by a maximum size of the LSB information.
 3. A non-transitory computer-readable storage medium storing a bitstream comprising: LSB information regarding POC information of a current long-term reference image of a current image, wherein the LSB information regarding POC information is generated based on POC information of the current long-term reference image of the current image corresponding to the current long-term reference image of the current image, wherein POC information of the current long-term reference image of the current image is obtained by performing an inter prediction on the current image by using the current long-term reference image of the current image, and wherein the LSB information is information regarding a remainder value generated by dividing the POC information of the current long-term reference image of the current image by a maximum size of the LSB information.
 4. A video encoding method comprising: performing an inter prediction on a current image by using a current long-term reference image of the current image; obtaining POC information of the current long-term reference image of the current image corresponding to the current long-term reference image of the current image; generating LSB information regarding the POC information of the current long-term reference image of the current image; and generating a bitstream including LSB information regarding POC information of the current long-term reference image of the current image, wherein the LSB information is information regarding a remainder value generated by dividing the POC information of the current long-term reference image of the current image by a maximum size of the LSB information. 